The answer is because the pitching needs all the defensive help they can get, thus bring up a real OF who is a good defender in addition to a good bat. Whoever they call up won't sit the bench - he will take Braun's place in the starting lineup. Perez is fine for an occasional start, but I'd rather have the experience and athleticism of a Brinson/Phillips/Cordell. Perez has a nice arm, but the three CS OFs are, IMO, better defensively. It's a prime opportunity to get their feet wet and get the major league jitters out of the way. I'm wary of Cooper. Guy is all of a sudden slugging 140 points above his career? Seems like a fluke.