10-03-2017, 08:04 PM
I agree tackles is a bad metric. Some of it is dumb luck... how often is a play run towards you. And how often a play is run towards you may depend a bit in how poor a defender you are. That being said, when Blake Martinez led the league in tackles a couple years ago, we took it as a mark that he was a pretty good player ("had a nose for the ball"), so there is something to the stat on an individual level (especially among the front 7). And, obviously, on a team level, tackles = defensive plays - touchdowns surrendered so pretty much a lot of it will be correlated with pace of play and how many defensive plays a team is on the field for.
On the other hand, the success rate matters much more as a team defense than for an individual player. As WIM noted, you would expect a defensive back to get a smaller number of "successful" plays than a defensive lineman. But even among one position group (say, linebackers) you would expect differences based on assignments. A rushing or blitzing linebacker will pretty much either get a successful play (if they get to the QB) or they won't get a play at all (if the QB gets rid of the ball), whereas a covering linebacker who tackles the tight end just after they catch the ball is almost certain to get an unsuccessful play, even if it was a good one. Or consider a running play. If the defensive lineman stuffs the play at the line of scrimmage they get credit for a successful play. However, if he get blocked out of the play or the running back breaks their tackle and gets to the second level, the safety who saves the touchdown gets credited with an unsuccessful play. So, I think it is a poor metric to apply to an individual player, even though it does have value in evaluating team defense.
It is ultimately hard to evaluate Perez without figuring out what he is being asked to do in the context of the team defense. My instinct based on watching the defense is that there are probably better options on the team right now (albeit injured), but I don't think any stat could really answer that. I'd be interested to see how PFF grades him based on individual plays.
BC
On the other hand, the success rate matters much more as a team defense than for an individual player. As WIM noted, you would expect a defensive back to get a smaller number of "successful" plays than a defensive lineman. But even among one position group (say, linebackers) you would expect differences based on assignments. A rushing or blitzing linebacker will pretty much either get a successful play (if they get to the QB) or they won't get a play at all (if the QB gets rid of the ball), whereas a covering linebacker who tackles the tight end just after they catch the ball is almost certain to get an unsuccessful play, even if it was a good one. Or consider a running play. If the defensive lineman stuffs the play at the line of scrimmage they get credit for a successful play. However, if he get blocked out of the play or the running back breaks their tackle and gets to the second level, the safety who saves the touchdown gets credited with an unsuccessful play. So, I think it is a poor metric to apply to an individual player, even though it does have value in evaluating team defense.
It is ultimately hard to evaluate Perez without figuring out what he is being asked to do in the context of the team defense. My instinct based on watching the defense is that there are probably better options on the team right now (albeit injured), but I don't think any stat could really answer that. I'd be interested to see how PFF grades him based on individual plays.
BC