soft implies just that, soft and not physical while playing the game.
Passive, at least in this context, implies more that he is deferring to others which is very understandable for a rook with a reputation as a black hole coming to a team with other offensive options who is just trying to fit in and take good shots but not be too much of a black hole.
Now, they're asking him to be more aggressive, which is probably all Harrison needs to hear.