Depending on how many pitchers are carried, I have my doubts that the Astros can carry more than 4 outfielders...depending on other moves in the next month or so, I suppose. If you assume 4 back up positions on the roster, that means 1 catcher, 2 infielders, and 1 outfielder. With Wallace as a sub-par alternative as the back up to 3b, I am guessing that Greene and either Elmore or MarGo make the roster as infield backups. But I wouldn't be surprised if Luhnow uses rotating 5th starters between the ML roster and OKC in order to open up one more roster spot. That's why I think the 4th outfielder needs to be able to back up CF.