I'm sure others will have a different view point but in all my years of playing football i have always found that tackling hurts more than being tackle or trying to run through someone. I've just always felt that my potential for injury was higher while tackling. I'm not too concerned about Colin's "size" so to speak but more of his strength and level of fitness/flexibility. Most athletic injuries usually occur do to some combination of muscle inbalances, lack of flexibility, or just over all weakness in muscle groups. Unless he's already done irreparable joint or tendon damage adding some strength will help his injury woes.