I haven't been here all that long, but I think it's just reference to the old school baseball thinking that a player can be completely inept on offense and still be an asset to the team, hence "driving in runs with his glove."
He's gonna be hard to send down..... thankfully he doesnt chase certain pitches like certain other #20's ?? Patterson was 17 wasn't he? http://www.thediamondangle.com/archive/aug02/cubs/corey2.jpg