After the Hawks blocked 19 shots in two games in Atlanta, they produced only 7 blocks in the two games played in Milwaukee. While blocked shots don't completely encapsulate a defensive performance, there's clearly a trend here. The Hawks' interior defense was absolutely dominating during the first two games in this series, forcing the Bucks to make shots out on the perimeter in order to score at all. The threat of Josh Smith looming on the help side checked the aggressiveness of Jennings and Salmons, keeping from driving to the hole. For every Block in those first two games, there was another shot altered and missed as a result of the close-out defense.
What changed? As much as the Hawks try to convince you otherwise, it's more than just effort. Ignoring game 3 for a moment, during game 4 (in which they blocked only 2 shots) your Hawks were doing their damned best to stay in front of Jennings defensively, and weren't up to the task. The Bucks simply executed a better offensive strategy, utilizing screens on the perimeter to force the Hawks into a switch. I'm not going to pretend that Kurt Thomas was not setting borderline illegal screens every other trip down the floor for the Bucks, but the Hawks still played directly in the Bucks' hand by sacrificing interior defense for more help on the perimeter. The problem with switching on every single screen is that, over a 7 game series, a team has plenty of opportunities to get past the novelty and gain practice attacking it.
There are circumstances where switching is absolutely necessary. If there's a really good pick, you switch instantly to prevent a good shooter from having an open look at the basket. You prevent open threes by letting the screener's man close out on the ball handler, and it helps against the pick and roll because both players are immediately accounted for. It also puts you in a good position to trap if you find a more marginal passer and ball handler. And knowing when the switch is on helps prevent the offensive player from faking into the screen and driving past his man while he's tangled up.
Switching on every screen is a bit problematic. It means that the offensive team does not need to set a particularly good screen in order to force a switch. This allows them to dictate their own match-ups with relative ease; guards aren't going to fight through screens, and the quickest players on the floor can pick who they want to attack. We've seen this repeatedly. Horford actually has great lateral quickness for his size, and he forced Jennings into some tough shots. Josh Smith is a bit more lacking in lateral quickness, even though he's good straight ahead speed. This isn't a significant problem for the Hawks, though, because both Smith and Horford do as well, or even better, at staying in front of the Bucks' guards as the Hawks' guards. In a lot of ways, the Bucks are missing out on the big bonus of this strategy by failing to repeatedly switch their bigs onto Bibby.
The big problem is the secondary effect: the help defense. When Jennings is driving and he's got Joe Johnson in front of him, Josh Smith is lurking on the help side to block his shot. And if it's not Josh Smith, it's Al Horford, who's a very good shot blocker in his own right. When you can set a pair of screens and get both of them out of the paint (they don't have to be on-ball screens; the Hawks will switch on off-ball movement as well) then the help is coming from JJ or Crawford or Bibby, who are not great help defenders. That's a huge drop off from having Josh Smith lurking in the paint, arguably the best help defender in the Association. And when JJ is initially on Jennings, he ends up mostly eliminated from helping as well since he's switched out high on the screener, out of position to come down and help. He's much preferable to Crawford or Bibby as a help defender-essentially non factors
What the "Switch every screen" strategy seems to be aimed at is keeping players from having to think too much. When Woody was coaching a much younger team, it might have been best to get them switching on every screen to avoid complete lapses. Guys like Smith and Marvin, who were very raw (but extremely talented) players when they entered the NBA had one less thing that they'd need to learn to do. Instead of learning how to read the screen to see if would dislodge the primary defender, and to determine what position they needed to be in, they simply had to build the reflex of popping out on the switch. It might help serve to smooth the transition for players making a huge jump from prep ball to starting on an NBA roster.
I can't say with any certainty if this is where the idea originated, or if Woody had such a motivation for implementing it. We've looked at it in the past and seen how it can lead to lazy feet sometimes when there's a switch with minimal movement involved. That certainly hasn't been the case this series, as the Bucks are getting their switch and then very quickly forcing the action by driving into the paint. Two screens to get Horford and Smith on the perimeter, and they've greatly reduced the threat of having a shot blocked or altered in the paint. I can't criticize the job that Horford and Smith are doing on the perimeter because Jennings and Salmons have made some really tough floaters in the last two games, and asking the pair of them to guard 4 players is stretching their capabilities.
What I would love to see from Woodson in game 5 is to actually play some zone defense. Maybe an entire game worth of zone defense. It should help force the Bucks into taking more jumpshots, which has not at all been their strength in this series. It also helps cover up some of the gap in quickness on the perimeter by forcing the Bucks to attack spots instead of specific players. Normally, this is not recommended against a team like the Bucks, who lack an interior offensive presence that they want to work through. It limits some of the mismatches, which can be detrimental to the better team. But the mismatches on the perimeter are more costly, and having our best help defenders in the appropriate position should really help disrupt the lay-up drill we saw during the quarters 2 and 3 of Game 4.