In the first half of this study, I analyzed the conditions that would be necessary for a true “league without centers” – an ultimate small-ball paradise without any traditional big men. We found that the offensive value of high-efficiency finishers would be difficult to replace without an unimaginable increase in three-point shooting accuracy.
To this point, we haven’t yet analyzed the point at which most teams would not use a traditional big man for defensive purposes. While the foregoing analysis has laid out what I see as the necessary conditions for a big man to have no purpose on offense, the question remains as to what shape such conditions might take on the defensive end. When would it not make sense to have a big man on the defensive end?
It is difficult to come up with a really satisfactory method to analyze this question. The best shot in basketball is the shot at the rim, and these are the shots that big men challenge most often. Most analyses of defensive data suggest that big men make a significant defensive impact, and the statistical results track with the internal logic of the game: big men protect the most vulnerable area of the floor, so of course their impact (positive or negative) is noticeable. Maybe the answer is the same as before – if another shot ever becomes as valuable as a shot in the restricted area, then it won’t make sense to purposely play a defender who is too slow to defend on the perimeter.
A better method to evaluate the question might be to ask how much value big men surrender to the opposition when they are forced to defend on the perimeter (as a result of switching a screen, trapping the ballhandler on a pick and roll, rotating onto a faster player who drives past them, etc.). With this data in hand, we could then compare it with an estimate of how much value big men generate for their own team by preventing points near the basket. Theoretically, it would be fairly simple to determine the tipping point using this method – once big men give up more value than they produce, it would not make sense for most teams to play a big man most of the time.
Unfortunately, there are some obstacles to carrying out this methodology. The publicly available data does not tell us how often a player switches on screens. The best we can do is see how often big men end up defending a shot by the handler in a pick-and-roll play or a handoff. Unfortunately, there are very few plays recorded this way, since it requires that the original on-ball defender be totally leveled by a screen or out to lunch. As such, a number of possessions in which the big man’s lack of quickness hurts his team do not appear in this data; they are instead marked as plays against the original on-ball defender. Due to the small number of plays, the total effect looks negligible. In actuality, the effect is substantial, but the way the data is collected screens out (pun intended) most of the effect we want to study.
Another way to study the issue might be to compare the impact of big men on opponent shooting by distance, assuming that interior defenders would make a positive impact on shots closer to the rim and negative impact on shots farther from the rim. Analyzing the data from last season, we see that big men yielded a 56.3% opponent field goal percentage on shots within six feet of the rim, while the league average on such shots was 62.2%. Since the leaguewide average includes shots defended by a big man, it is fair to say that a traditional big man reduces opponent shooting effectiveness by at least six percent near the basket. It needs to be clear that this is a titanic difference. Six percent is greater than the difference in Opponent True Shooting % between the best defense in the league and the worst defense in the league last season.
How much damage do big men do defending jump shots, relative to the value they add defending inside shots? The raw field goal percentage on shots from beyond 15 feet is slightly higher (worse) for shots taken against big men than for the league average by a margin of 37.4% (shots against bigs) to 36.7% (all shots longer than 15 feet). This gets tricky fast, though, because the effective field goal percentage yielded by big men on these shots is actually lower (better) than league average. It’s not hard to figure out why that is so: big men are more often defending other big men who are relatively poor jump shooters. It’s a major point of the game plan for many defenses to do precisely this: to have their big man defend either an inside player or the worst shooter on the opposing team, so that the big man can leave the weak shooter to help in the paint. As a result, many of the three-pointers taken against big men are attempted by poor shooters.
Thus, shots outside of 15 feet taken against big men are a bit more likely to go in than shots from the same range taken against smaller, quicker players. This is not really what we want to know, though; because of the bias in the data caused by big men defending weaker jump shooters, the negative impact of big men being forced to defend opponents farther from the hoop gets minimized. As such, we can’t really compare it to the positive value produced by big men that results from forcing misses near the rim.
Even if we were to try and “make it even” by assuming that big men actually increase opponent shooting percentage by 6% on shots beyond 15 feet just as we know that they decrease opponent shooting percentage by at least 6% on shots within 6 feet, the difference in total value added vs. value lost is still sizable. Last season there were 19,119 shots within 6 feet taken against a big man, while there were only 13,488 shots from outside 15 feet taken against big men – a difference of roughly five and a half thousand shots. Even if big men give up as much value per shot on outside shots as they contribute per shot on inside shots, there would still be no justification for a league without centers.
Personally, I think even the above thought exercise is suspect. If traditional big men really hurt their teams’ perimeter defense that much, I would expect it to show up a bit more in the data we have, even with the effect of the bias inherent in that data. The positive contribution of rim defenders to their team’s defense, on the other hand, is readily apparent in even the most basic data.
Defensively, then, there is little evidence that we are actually headed toward the extinction of the traditional big man. The area around the rim is too precious for most teams to dispense entirely with an interior presence. Even with the limitations in the publicly available data, it is difficult to conceive of a realistic set of circumstances under which teams would not benefit from having a traditional big man on the floor for defensive purposes.
On balance, I do not see compelling evidence that traditional big men will disappear from the game. While traditional bigs have been replaced and had their roles diminished, a trend that will no doubt continue, it does not appear that the trend will continue to its end point. Put another way, the trend will reach a point at which the very analytics which are accused of decreasing the role of the traditional big man will end up coming to big men’s defense by proving that beyond a certain point, teams are giving up far more by not playing centers than they are gaining by playing without a center.