Neither one looks good in CF to me. So far it seems like there have been a couple of balls Happ should have caught in CF. Small sample size, of course, but in center Happ is at -1 DRS in 19 innings, Jay is at -4 DRS in 79.2 innings. Happ looks plenty good for a corner outfielder though, I just don't think he has the defense for CF as his primary position. Statistically, only Heyward has been a plus center fielder this year (2 DRS in 66.1 innings) and for his career (9 DRS in 470.1 innings), even Almora is at -1 DRS. Maybe they're just trying to see if Happ is good enough to backup CF.