Adrian Peterson has a torn meniscus, which is expected to keep him out until at least December. Given Peterson’s age — he’s 31, with his half-birthday coming yesterday — it’s reasonable to start thinking about whether the end is near for Peterson.
In his last 8 games (excluding playoffs), he rushed 150 times for 529 yards (3.52) with 5 TDs, one fumble, and 26 first downs. Prior to this stretch, Peterson had averaged 159 carries, 786 yards (4.95), 6.5 TDs, 2.24 fumbles, and 37 first downs. Given his performance in the one playoff game during that stretch (23 for 45 with one fumble), including that would only make the numbers look worse.
I came up with a relatively simple adjusted rushing yards metric to measure running back performance (note that in the formula below, rushing TDs are actually worth 20 yards because all rushing TDs are also rushing first downs):
(rushing yards + rushing first downs * 9 + rushing TDs * 11 – fumbles *30) minus (rush attempts * 5)
This is basically a mix of rush efficiency and rush quantity: we take rushing yards, add some other information, and then provide a penalty for each attempt used. The graph below shows Peterson’s game-by-game results for his career, along with, in black, a trailing-8-game average: [click to continue…]