Came across this on a post on Bill James Online:
Highest first pitch swing percentage in 2012:
1. Josh Hamilton, 47.0 percent
10. Bryce Harper, 38.1 percent
Lowest first pitch swing percentage in 2012:
1. Martin Prado, 6.9 percent
4. Mike Trout, 7.7 percent
I don't think there's a whole lot to read into those numbers, as there are many different ways to skin a calf. In fact, the phenoms ended up with similar walk and strikeout rates:
Harper: 9.4% walk rate, 20.1% K rate
Trout: 10.5% walk rate, 21.8% K rate
Normally, too much aggressiveness on the first pitch could be a red flag, especially if it means a hitter is swinging at too many pitches out of the strike zone, lead to a lot of pitchers' counts a poor walk rate and/or weak contact. You know, somebody like Delmon Young, a guy whose poor approach has ruined his once promising talent. Harper swung at pitches out of the strike zone 34.9 percent of the time, which ranked 33rd-worst out of 143 qualified batters, so he's not in Young or Jeff Francoeur territory. Trout was at 26.5 percent, ranking 109th, and certainly that ability to swing mostly at strikes -- or lay off pitches outside the zone -- was a key to his success.
Two more notes on Harper. As his power continues to develop, he'll likely see fewer first-pitch strikes, so his ability to lay off bad balls will be a key to his growth as a hitter. The Nationals, however, seem to preach a certain amount of aggressiveness at the plate, as Ian Desmond and Danny Espinosa also ranked in the top 10 in percentage of first-pitch swings. Now, all three are young players, so it's possible they can all mature yet as hitters.