Don't know who's to blame, but the US recruiting under Walters has been mediocre. In two seasons, they have found one above average player -- Leggett. Cotton may turn out to be another. But that's it.
Compare this with Mack, who brought in Matthews, Wild, Washington, etc and Walters and Co have performed poorly in this area.
Makes me wonder whether Hall is the main guy to blame for the bad defence, or if Walters shares some responsibility for failing to recruit better players.