After being selected in the 8th round of the draft (the second time he was drafted) by the Cubs in 2004, he worked through the minor leagues pretty quickly, and broke into the major leagues in 2007 with his first hit, against the Astros. Since then, he's provided nothing but disappointment in the major leagues. He's been through the Cubs, the A's, and now is getting a shot with the Red Sox.
So now he's jumped his way onto the 25-man roster, so what can he provide?
The first thing that this pickup says to me is that he is a utility player's utility player. Bill Hall was brought in to occasionally spell 2nd, 3rd, or right field. Since coming to the Red Sox, however, he spent quite a while as practically an everyday right fielder and is now, unless something more impressive comes along, our everyday second baseman until Pedroia gets back. Patterson, with his ability to play all three outfield positions as well as being a lefthanded batter who can play second base, appears to have taken over as the new backup to the backup.
Through the minors, he really looked like he might be something special. Through the minors, he managed to flash OPS' in the Cubs and As systems of between .817 and .931, all while stealing tons of bases and providing plus speed.
So far, however, he has been unable to translate the offensive ability into hitting off of major league pitchers. He has been significantly better against righties than lefties, but in neither case good enough to really knock Bill Hall off the lineup without proving he's in a pretty decent hot streak first. In the minors, he was pretty good against righthanded pitching, but in the majors, he's merely been not quite as bad.
It is worth noting that his BABIP has dropped .121 points this year, although that went along with a 4.3% drop in LD% so far. Hopefully both those numbers right themselves to careers norms, but they still won't be terribly impressive. His swing tends to pull, despite little power, which probably won't play terribly well at Fenway.
Despite this, the positives are that he at least looks like a good defender at second, and probably at least a decent outfielder in all three outfield positions. He does provide positional versatility. Unfortunately, he provides versatility for a guy whos bat you don't want to see in the lineup.
If he comes to Fenway and finds that Dave Magadan can work wonders with his swing, he might find himself platooning with Bill Hall at second base until Pedroia is back. Otherwise, he'll find himself in the same position Hall has been in- backup everyone hopes is not playing, in almost every position possible. In any case, it's hard to imagine his future with the Red Sox lasting longer than Pedroia's injury.