Thursday, September 26, 2013
NFL roster stability usually equals success
By Dean Oliver & Hank Gargiulo, ESPN Stats & Info
Your fantasy football team changes every year, but so do the players on real NFL teams. Their rosters turn over both in the offseason and in the regular season, usually due to injuries, though trades (like the recent one involving Trent Richardson) can happen.
“Roster stability” is a metric to track how much personnel changes from season to season based on work done in basketball by Dr. David Berri at Southern Utah University, and counts how many plays the players on the roster played last year and this year. Raiders QB Terrelle Pryor, who was on the roster last year but barely played and is now playing full time, represents a good amount of instability because he didn’t play much last year.
What “roster stability” captures is something about the philosophy of the team. Teams that are pretty stable year-to-year usually consider themselves to be in good shape, either because they were good last year or because they think the building blocks were already in place. You can see this with many of the top teams on the list. The Bengals, Vikings, Redskins, Texans, Seahawks, 49ers and Falcons were all successful last season and they kept a good number of their players around for this year. Note that keeping the same players doesn’t mean the same results, as both the Vikings and Redskins haven’t won a game yet this season.
On the other hand, teams at the bottom of the list are teams that wanted to change things up. The Raiders weren’t very successful last season and they particularly changed up their defense, which ranked 28th by expected points added.
A couple notes:
• The Bears, Chiefs and Cardinals all changed head coaches, changed a lot of offensive personnel, and have seen improvements offensively. The Bears, in particular, changed a significant part of their offensive line (their offensive line unit stability is 20 percent, the lowest in the NFL), which was considered important for protecting Jay Cutler. Now they have the second-lowest sack rate in the NFL after being 27th last year.
• The Patriots receiving corps, widely publicized for being so dilapidated, ranks 31st in stability at 30 percent, ahead of only the Jaguars. Their overall offensive stability is 21st. Note that their defensive stability ranks third, and their defense ranks second in the NFL in expected points added.