The Deflation of Rebounding

I’ve thought about it in the past, but it wasn’t until the question was actually posed that I decided to actually look into the situation. It has sort of come up over the past few months as fans dissected and debated if Melvin Ejim should have his jersey retired. How did Zaid Abdul-Aziz (Don Smith) average so many rebounds?

There are a multitude of variables at work here and sadly, a lot of them are undefined as stats were different “back in the day”. Heck, in the 1951-52 and 1952-53 seasons it wasn’t even deemed necessary to track the number of attempted field goals or free throws (don’t ask why it was done the two season prior and then halted for those two seasons, because I have no idea).

When you look at rebounding numbers though, it is staggering how many of the best individual best seasons were long before my time (born in 1984). 14 times an Iowa State player has averaged ten or more rebounds in a game for a season, the most recent being in the 1978-79 season (Dean Uthoff). When you ramp up the sample to include all seasons where a player averaged at least nine rebounds per game you can find 32 cases but only eight of them have been since 1990 (Jackson Vroman in 2002-03 & 2003-04, Craig Brackins in 2008-09, Melvin Ejim in 2012-13, Marquis Gilstrap in 2009-10, Royce White in 2011-12, Loren Meyer in 1993-94 (though he only played 12 games at the start of the year due to injury), and Victor Alexander in 1990-91).

So, what is the deal here? Are all the great rebounders in our past? Or is it more likely that something else is going on? Were there just more rebounding opportunities? Sadly as I mentioned above our research options to discern why more or less shots were taken due to offensive rebounds and turnovers are extremely limited. Turnovers weren’t even tracked until 1982-83 and offensive rebounds aren’t included in my data…I’m not sure when they first would have been tabulated.

Aside from turnovers limiting shots and offensive rebounds adding shots, did teams just play more of an up-tempo style? And what role do free throws play in all of this?

Let’s find out.

(Note: All the data below is for Iowa State shooting only. I made the assumption that the general trends I found here for Iowa State would carry over to most every other NCAA team.)

I made a chart for every Iowa State season from 1949-2014 (minus the two seasons where shot attempts were not tracked) to see how the number of attempts has changed over time. The blue line shows the field goal attempts per game and the red line the free throw attempts. As you can see, in the past 65 years the number of total shots has decreased gradually.

fga fta per game 1949-14

The results aren’t staggering that the total number of shots is on the decline, though. So I made another chart.

isu shooting percentages 49-14

The above chart is Iowa State’s team shooting percentage from both the free throw line and from the field since 1949. Probably not so surprisingly, the percentages have slowly improved over time. Could it be that there are just fewer rebounds available now because not only are fewer shots taken but a higher percentage of shots are successful? Again, the change over the past 65 years isn’t jaw dropping enough to convince most that the better shooting is limiting rebounds, but what if we combine these two charts?

By looking instead at the number of attempts and success rate from the field and the free throw line we can deduce how many rebounds were available, on average, in a given season. At least at one end of the court because I do not have the data for opponent’s shooting success.

The next chart is the average number of misses per game in the given season.

total misses per game 49-14

(Note: The data from the charts is in a sortable table at the bottom of this column.)

As expected, there is a much more drastic decline here. The number of available rebounds has obviously declined, substantially. Shot attempts have gone down, shooting percentages have gone up and that has led us here. However much these numbers are affected by style of play or turnovers is unknown, but the end result can be clearly seen.

There is one other crucial element, though. With free throw misses it cannot be determined which misses were live ball misses available to be rebounded for at least part of this exercise.

Up until the 1954-55 season every single foul resulted in one free throw. Here, a miss can be rebounded and a make cannot be in every case. In that 1954-55 season a new rule meant that every foul resulted in a “one and one” trip to the free throw line. To earn the second shot you must make the first. In this case, every miss is also a live ball available to be rebounded.

With that new rule, the old rule that gave two free throws if a foul was committed in the last three minutes of either half or overtime was eliminated. From 1949-1954 of this data there are surely some instances where missed free throws were not live balls, we just have no idea exactly how many.

In 1972 the single free throw granted for any of an opponent’s first six fouls were removed and a team simply shot “one and one” from the seventh foul and beyond. In 1983, the same was true except for fouls in the last two minutes of either half or overtime resulted in two free throw attempts. Finally, in 1990 the system was put into place that we know today.

Through all of this though, I haven’t found any concrete answers on how shooting fouls have been handled over time. If they were treated like common fouls or if they resulted in two free throws regardless gets murky.

But, the point of all of that jargon is one thing. Up until 1972, any foul resulted in free throws and the vast majority of those would have been live balls to be rebounded.

What I’m saying is that while Bill Cain averaged a staggering 15.2 rebounds per game in 1969-70 (the record at Iowa State) he likely had many, many more opportunities than say Melvin Ejim in 2012-13 when he averaged 9.3 rebounds.

This is turning a bit into fuzzy math, but since I don’t have opponent numbers let’s just play around and see what happens. In 1969-70 the Cyclones averaged 43.8 missed shots per game and every miss would have been a live ball (sans the above unknown with how shooting fouls were handled, but I think this is correct). Let’s double that to simulate an average number of misses from Cyclone opponents to arrive at 87.6 available rebounds per game. When you divide Cain’s rebound per game average you find that Cain grabbed an approximate of 17.38% of rebounds in that season.

In 2012-13, the Cyclones missed an average of 38.03 shots (where decidedly fewer of those could not be rebounded if they were the first of two free throw attempts) if we double that we get 76.1 total shots missed. Divide Ejim’s 9.3 rebounds per game and you arrive at 12.24%.

Here is where the mental fudge factor has to come into play. Obviously, Ejim’s percentage is lower but how much of that is due to a greater number of free throw misses being in dead ball situations and how does that affect the numbers overall? We don’t know and we never will.

What is interesting though is that in the 1969-70 season Cain grabbed 40% Iowa State’s rebounds which is still far and away better than Ejim in 2012-13 when he grabbed 24% of his team’s rebounds. And that same trend from above with most of the guys at the top of that list from prior to 1990 is still pretty true. But instead of just eight guys in the top 32 there are 11.

So after all of those calculations and charts above, how is this still happening? Maybe they were better rebounders?

There are a couple of other minor factors that come into play here as well. One of which I can give some answers and one of which I can’t because I’m not old enough.

First, and this isn’t a matter of Ejim being undersized so much as someone like Cain being oversized but the average height of Iowa State’s roster was three inches taller in the 2012-13 season than it was in the 1969-70 season while Ejim and Cain are both the same height at 6’6”. The point being that “back in the day” a taller player had a bigger advantage than current day because players just weren’t as big.

Second, is the one where I would need help. I have to wonder and believe that players 50 years ago played more and rested less over the course of the games. I don’t have minutes played that far back, so I cannot prove it, but pragmatically it would seem to be true and explain what is going on. For one thing, there were fewer better players then and very subjectively, doesn’t it just seem like they must have played a greater majority of the game?

That is probably the loosest you will ever see me attempt to help validate a conclusion. We can’t pinpoint the exactness of the situation or the definite “why” to answer the outrageous rebounding numbers of the past, but I think a case was laid out here to explain it pretty well with the data that is available to me.

Does that mean that Melvin Ejim was just as good of a rebounder as Bill Cain? Maybe. It’s still inconclusive but I do think we can say now that the gap isn’t quite as large as I once thought.

Conf.Team% of Poss w/ 20+ Yard TDFG %% of Poss w/ PtsPoss w/ TDsPts / PossPts / Gm
ACCFlorida State14.7795.4559.6647.734.1151.64
Big 10Ohio State16.8590.0051.6946.633.5845.50
SECTexas A&M12.2076.9250.6144.513.5144.23
Pac 12Oregon14.5371.4348.8443.023.4445.46
Big 12Baylor19.6062.5048.7441.213.4252.38
SECAlabama15.4465.0047.6538.933.3338.15
AACLouisville12.5080.0049.3135.423.1735.15
IndyNavy11.4378.5749.2941.433.1133.54
C-USAMarshall12.5768.7545.5539.793.0942.14
C-USAEast Carolina8.2861.5447.9338.463.0940.15
MWCFresno State10.8768.7544.5738.593.0743.38
SECLSU15.0392.8647.7139.223.0435.77
SECAuburn12.9771.4344.8636.762.9939.50
MACBowling Green11.0481.8246.0134.972.9934.79
MACNorthern Illinois10.2258.8247.3136.562.9839.64
SECSouth Carolina13.2583.3347.6837.752.9334.08
ACCGeorgia Tech11.4671.4343.3136.942.9035.08
SECMissouri11.1172.0044.4434.922.9039.14
MACBall State10.9879.1747.4036.422.9038.54
SECGeorgia6.6792.3149.0934.552.8936.69
ACCClemson13.1987.5043.4135.712.8740.15
Pac 12Arizona State9.1883.3345.4132.652.8439.71
AACUCF8.8187.5047.1733.962.8334.62
Pac 12Washington8.0093.7542.8634.292.8237.92
Big 10Indiana13.9481.8242.4236.972.7938.42
Pac 12UCLA8.7266.6743.6035.472.7936.92
MACToledo11.8995.0044.7631.472.7733.00
MWCNew Mexico13.3866.6740.1434.512.7732.75
Big 12Kansas State12.7477.7841.4032.482.7533.23
Pac 12Stanford12.7376.9243.0330.912.7432.29
Big 10Wisconsin10.8466.6742.7734.342.7334.85
MWCBoise State8.3389.4743.3333.892.7137.54
ACCMiami (Florida)10.4376.4738.6530.672.7033.85
Sun BeltLouisiana-Lafayette11.0464.2938.6533.132.6933.77
ACCNorth Carolina10.0073.6838.1329.382.6632.69
Big 12Oklahoma State6.6761.1136.9231.282.6139.08
Sun BeltTroy10.1973.3339.4932.482.6134.08
MWCColorado State11.7987.5042.0531.282.6036.21
Big 12Oklahoma8.4888.8940.6126.062.5932.85
Sun BeltWestern Kentucky4.9081.2541.2632.172.5930.83
Pac 12Oregon State5.7170.0038.2930.292.5834.77
Pac 12Arizona8.8263.1637.6530.592.5633.46
Big 10Michigan6.5972.0039.5228.742.5132.23
AACCincinnati11.8341.1837.2833.142.4732.08
MWCSan Jose State15.1981.4843.0429.112.4632.42
ACCDuke7.4968.4235.8328.882.4532.79
C-USANorth Texas9.9462.5033.3327.492.4231.85
Big 12Texas Tech7.2585.1939.9027.982.4135.77
Big 10Illinois10.1470.5937.1629.052.4129.67
SECMississippi13.2566.6737.3527.712.3530.00
Big 10Nebraska8.4792.8635.0327.682.3431.92
MWCUtah State5.7969.2336.3226.842.3431.79
SECVanderbilt7.1478.9538.1029.172.3330.08
Big 10Michigan State10.1786.3636.7225.992.3229.36
IndyNotre Dame9.8074.0738.5625.492.3127.23
C-USAMiddle Tennessee6.7575.0033.1325.772.3129.00
AACHouston7.9873.9135.1126.062.2933.15
Sun BeltSouth Alabama7.7978.2638.3126.622.2929.42
Sun BeltArkansas State5.9283.3335.5026.632.2429.15
MACBuffalo6.2565.0033.5226.142.2430.31
Pac 12USC11.8368.1834.4126.342.2429.71
MWCUNLV9.2052.6335.6329.892.2429.92
Pac 12Washington State7.7380.0034.2525.412.2331.00
MWCAir Force6.7784.6236.8428.572.2324.67
MWCWyoming9.4757.1431.9529.592.2231.25
Big 10Minnesota6.6277.7832.4523.182.2125.69
MWCSan Diego State10.2350.0032.3927.842.2029.77
ACCBoston College13.41100.0037.2025.002.2027.69
SECMississippi State7.3247.6234.7628.662.2027.69
C-USARice5.7966.6734.2126.842.1829.64
MACOhio4.8575.0033.9423.032.1627.38
MWCNevada3.9582.3535.5326.322.1326.92
C-USAUTSA7.5957.8932.4124.832.1225.58
ACCPittsburgh7.4177.7833.9525.312.1126.31
IndyArmy5.7672.7333.0927.342.1124.42
C-USAUAB11.3366.6734.6724.002.1026.25
Big 10Penn State6.6765.2235.1526.062.0828.67
AACRutgers5.4268.4231.3323.492.0826.54
Big 10Iowa5.4572.7332.1222.422.0726.31
Big 12Texas10.2790.9134.0523.242.0629.31
Pac 12Utah8.0985.0033.5323.702.0229.17
IndyBYU8.2180.7732.8222.052.0130.15
AACTemple9.4033.3328.8626.852.0124.92
C-USAFlorida Atlantic6.9264.7130.1923.271.9926.42
Big 10Northwestern4.4092.0033.9619.501.9726.17
AACSMU5.4985.7132.9321.951.9626.75
MACCentral Michigan6.1670.5929.4521.231.9123.25
ACCMaryland7.6184.0030.9819.571.8526.15
SECTennessee3.2382.3528.3919.351.8523.83
Sun BeltTexas State5.1060.0026.7521.021.8323.92
Pac 12Colorado10.1870.8328.7418.561.8325.42
C-USAUTEP7.5946.6726.2121.381.8021.75
C-USATulane5.0369.5727.9318.991.8024.77
SECArkansas4.3581.2530.4321.011.8020.67
MACKent State7.8655.5628.5721.431.7820.75
MWCHawai'i9.5253.8526.4622.751.7427.42
Big 12West Virginia7.1473.9128.0218.681.7426.33
Big 12TCU4.6077.7827.5919.541.7325.08
SECKentucky7.5385.7128.7720.551.6820.50
Big 12Iowa State6.2165.0027.1219.771.6824.83
ACCVirginia Tech5.7157.6927.4318.861.6722.54
ACCNorth Carolina State6.6382.6128.3116.871.6522.83
SECFlorida4.3854.5527.0118.251.6518.83
Sun BeltLouisiana-Monroe6.7955.5622.8419.751.6522.25
ACCSyracuse4.9564.7126.9220.881.6222.69
MACAkron7.3356.2526.0020.001.6120.17
AACMemphis0.6888.8926.5315.651.5919.50
MACEastern Michigan4.7954.5522.6018.491.5518.83
IndyNew Mexico State4.9183.3325.7719.631.5420.92
Pac 12California6.0185.0026.7817.491.5123.00
C-USATulsa2.9684.2125.4415.981.5021.08
AACConnecticut4.8262.5022.8916.871.4920.58
C-USALouisiana Tech1.9178.2626.7515.291.4619.17
Sun BeltGeorgia State6.8866.6721.8816.881.4118.75
ACCWake Forest4.4666.6721.0215.921.4018.33
ACCVirginia3.2878.9522.9514.751.3019.75
MACWestern Michigan3.7580.0023.7513.751.2917.17
IndyIdaho4.6258.8221.3915.611.2618.17
Big 10Purdue4.0550.0018.2414.191.2114.92
C-USASouthern Mississippi4.0555.0020.2313.871.1817.08
AACSouth Florida2.6878.2619.467.381.1113.75
Big 12Kansas3.9864.7118.1811.931.0515.33
MACMassachusetts2.7663.1617.939.660.9711.67
MACMiami (Ohio)1.9663.6413.078.500.769.75
C-USAFlorida International0.6564.2914.198.390.759.75
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