As we all know Tillson is very good positionally and for breaking up play but his passing lets him down and when he is in possession the opposition put pressure on him because he is likely to give the ball away. Croll as a centre back makes mistakes, but playing infront of the back four they won't be so costly, he can play a good pass and is comfortable in possession of the ball and could equally break up play and his fast enough to make up for any positional senses Tillson has.