The Knicks are a poor defensive team (24th out of 30 in points allowed per 100 possessions in ’07; 26th in ’06 with more or less the same roster). Conventional wisdom has it that New York’s defensive ineptitude is due in large part to a porous interior defense, where Eddy Curry is a poor rebounder and shotblocker, David Lee is slow to rotate, and the departing Channing Frye was soft. Many worry that the interior D is only going to get worse with Zach Randolph and his poor defensive reputation joining Curry, portending an even weaker defensive squad in 2008.
With all that in mind, the following quote from Isiah Thomas regarding the Randolph trade is more than a little surprising, even though by and large it seems to have gone unnoticed:
I think Zach is a prideful defender right now and I think, as a team, we?ll get better as a defensive unit. Again, because I think we?ll defend the three-point line better than last year. We don?t necessarily give up a tremendous amount of points in the paint. We usually outscore teams in the paint, but we got hurt last year defensively because of the three point line. I?m not necessarily looking to improve our interior defense as much as I am trying to improve the defense on the three-point line. We have to get better on the perimeter. That?s where we had problems last year.
No Knicks fan is going to argue that New York did a poor job defending the perimeter last season. But curiously, Thomas contends that the interior defense is not a key area of concern. But that can’t be right, can it?
This matter bears a closer investigation. Fortunately, we can get a pretty decent picture of how well the Knicks defend different regions of the court using data from 82games.com. (Not all of the stats mentioned here are directly available at 82games.com, but they can be calculated from stats available at 82games.com and basketball-reference.com.) In particular, we can look at how well the Knicks defend shots in the paint, 2 point jumpers, and 3 point attempts. There are a couple of different components we can look at for each portion of the court: how often the opponent tends to shoot there and how well the Knicks defend field goals attempted there. Combining those two components, we can figure out how many points the average Knicks opponent gets from each region of the court per 100 field goal attempts. These data for the 2006/07 season are plotted in the graph below in standardized form, in order to give a side-by-side comparison of how the Knicks’ performance on each measure stacked up against the rest of the league.
The data seems to support Thomas’s claim. It seems the Knicks actually did do a good job of defending the paint in ’07. In actual fact, New York was not very good at preventing opponents from scoring once they got in position to get a shot up in the paint. However, this weakness was more than compensated for by the sheer paucity of field goal attempts in the paint by Knicks opponents. Only the Rockets allowed a lower proportion of inside field goal attempts than the Knicks. And in terms of points in the paint per 100 FGA, only the Rockets (3rd in overall defensive efficiency), Bulls (1st), Heat (8th), and Spurs (2nd) were stingier. That is impressive company.
Still, something doesn’t seem quite right. The 4 teams that allowed fewer points in the paint per 100 FGA were all strong defensive teams overall with strong shot blocking presences. Neither of those things can be said for the ’07 Knicks. All 4 of those teams were also in the top 7 in eFG% allowed in the paint, which makes for a natural story: these teams were very good at defending field goal attempts in the paint, thus dissuading the opposition from attempting shots in the paint to begin with. Such a natural explanation for why the opposition attempted so few shots in the paint is not on offer for the Knicks, since they were among the worst at guarding inside shot attempts. This raises one’s suspicion that perhaps the Knicks allowed so few shot attempts in the paint for some reason other than good interior defense.
For instance, perhaps the Knicks just fouled the opposition a lot whenever they got near the rim. This would be poor defensive practice, but it would also have the effect of reducing inside FGA by the opponent. But this excessive fouling in the paint hypothesis doesn’t seem tenable. The Knicks were right at the league average in terms of opponent free throw attempts per 100 possessions, and at the center / power forward positions they accumulated only 0.4 fouls per 100 possessions more than the league average.
Another possibility is that the Knicks did a lot of switching, doubling, and rotating to try to compensate for their poor interior defensive eFG%. Such a tactic could have the effect of limiting interior FGA while leaving the perimeter vulnerable. But is this consistent with the data? The Knicks certainly got crushed from the 3 point line. But they actually did a pretty good job at defending the 2 point jumper, holding opponents’ eFG% below the league average and allowing them to shoot a higher proportion of 2 point jumpers than the league average. (Allowing more 2 point jumpers is actually a good defensive tactic on the whole, since they are the lowest percentage shots available on the court.)
It turns out that this pattern of data is consistent with league trends for the ’07 season. For the league as a whole, defensive eFG% in the paint was significantly correlated with opponent 3 point attempts (r = .42, p = .02), opponent 3 point eFG% (r = .53, p = .003), and opponent points per 100 FGA coming from 3 pointers (r = .52, p = .003). In other words, the teams that defended the paint better also tended to defend the 3 point shot better. However, the correlations between interior defensive eFG% and 2 point jumper attempts and eFG% fail to reach statistical significance. That is, at least in ’07, there was no relationship between how well teams defended the paint and how well they defended the 2 point jump shot.
On the other hand, on a league-wide scale, the proportion of interior FGA allowed was not correlated with interior defensive eFG% and also was not correlated with opponent % FGA and eFG% for 2 and 3 point jumpers. This does not fit so nicely with the hypothesis that the Knicks surrendered so few interior FGA because of a swarming, scrambling interior D that left the perimeter vulnerable. It is possible that the hypothesis is correct nonetheless, and the Knicks were just idiosyncratic in terms of how they defended the paint. But it is also possible that, for all their defensive weaknesses and warts, they were doing something right in order to limit opponent FGA in the paint. So although we may be strongly suspicious of the appearance that the Knicks defended the paint well in ’07, the data presented here does not categorically rule out the possibility that there was some largely unrecognized but positive component to New York’s interior D that allowed them to limit interior FGA, and thus interior points per 100 FGA, by the opposition.
However, the idea that New York’s atrocious defense of the 3 pointer is linked to their poor interior defensive eFG% seems a bit stronger. Not only is this idea consistent with conventional basketball wisdom, but it is also consistent with league-wide statistical trends in the ’07 season. The worse teams defended the paint in terms of interior defensive eFG%, the worse they tended to defend the 3 point shot. (Of course, correlation does not imply causation, but there are independent, observational reasons for believing that a poorer interior defense could lead to a poorer perimeter defense.) The Knicks had a poor interior defensive eFG% and were among the very worst at defending 3s. So if the Knicks are to shore up their defense of the 3 pointer, it could very well require a fortified interior defensive eFG% (e.g. by way of better shot blocking and quicker defensive rotations). If the team focuses on improving 3 point defense while largely neglecting to focus on bolstering the interior defense, as Thomas’s quote suggests, the returns on perimter D could be fundamentally limited.