Saturday, December 27, 2008

Interceptions and Success

Advanced NFL Stats notes that interceptions are part of the game, and you can go too far trying to avoid them:

"While a lack of turnovers certainly helps win games, if it becomes a passer's primary goal it could be harmful.

"Interceptions are a part of the bargain, a natural consequence to throwing the ball. You can guarantee zero interceptions by playing in an extremely conservative way, tossing short passes, taking sacks, or throwing the ball away anytime a defender is in the same zip code as the receiver. You can minimize interceptions, but you'll lose every game doing it."

Which suggests to me that an extremely low INT rate isn't the sure sign of an elite QB.  Furthermore, as Bill Barnwell of Football Outsiders pointed out in warning fantasy footballers about David Garrard, a low INT rate is often lucky, and will likely fluctuate the next season.  This means if you rank QBs by their ability to avoid turnovers, you'll have a lot of fluctuation from year to year (suggesting further it's not the best way to evaluate the quality of the QB).  For example, this season Chad Pennington is #1 and David Garrard is #19 on Dave Berri's ranking, which heavily punishes turnovers.  Last season at the same time, David Garrard ranked #5 and Chad Pennington ranked #23.  Pennington's INT rate flipped from 3.5% to 1.6%; Garrard's INT rate flipped from o.9% to 2.2%.    If your system puts QBs who avoid turnovers at the top, it will fluctuate a great deal, for as Barnwell points out, a excessively low INT total is usually followed by a "major correction."  Berri's system may accurately assess a QB's performance (his existence), but I don't think it gets at the QB's inherent quality (his essense).  Football Outsiders is probably better at that (though in my opinion, Football Outsiders' statistical analysis is better at assessing team quality than individual player quality).

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