It hasn't received much attention, but Brodney Pool has greatly elevated his level of play since Jim Leonhard was injured. In the time since, Brodney is averaging 5 tackles per game. He was averaging 2.41 before Leonhard left the lineup. Leonhard was averaging just a shade over 5 tackles per game while he was playing.
It would be one thing if these numbers were skewed because Brodney was getting toasted in coverage and tackling receivers after big plays. That hasn't been the case, though (open field tackle on Matt Forte, anyone?). Pro Football Focus says in the past two games, which is when Brodney shifted from free safety to Jim's strong safety slot, Pool is only allowing a completion on 37.5% of targets against him. That compares to Leonhard's 67.9% this season. Pool is allowing 8.3 per completion. Jim gave up 15 per completion. Pool has broken up 5 passes in the past 2 games. Leonhard had 4 defenses all season. Pool is making more plays against the pass. Brodney is giving up a little over half the yardage Leonhard allowed.
I'm not sure whether you can say it has all been about Leonhard leaving the lineup. The coaching staff may get some of the credit for lighting a fire under Brodney. He was benched against Cincinnati the week before Leonhard went out, and Mike Pettine called him out the week before the Miami game as a disappointment. Since then, the results have been excellent. Brodney has his only sack, his only forced fumble, and 3 of his 4 pressures since. Focus has him at 8 "stops" on plays constituting offensive failure in the past four weeks to Leonhard's during the season.
I guess the Jets missed the boat a bit when they signed Pool. They were looking for a replacement for Kerry Rhodes. Instead they got a guy whose talents might have been made redundant by Leonhard's presence and are now flourishing without him. In some ways, they are exceeding his.