Elvis Andrus followed up his rookie season of 2009 with an almost identical batting average and a 13 point improvement in his OBP. His power fell off a cliff however, from a low .373 slugging percentage to a poor .301. He went from 31 extra-base hits in 2009, including six home runs, to 18 with no home runs in 2010. His results on fly balls may hold the key to why this happened.
The following graphs show pitch frequency location, movement, and batted ball results on fly balls in 2009:
Here's the same chart for 2010:
The movement difference is subtle, but the balls are staying up and moving away from Elvis a bit more. He's also chasing pitches higher in the strike zone, balls tougher to upper cut. More balls moving away from him, where he's just getting under the pitch results in more flyouts the other way. He didn't pull anything deep in 2010.