Brown is just not physical at all. Granted he's tiny out there but nonetheless defenders just push him and he goes flying. I could be wrong but I think his drops are just him not being tough enough and he's worried about taking the hit. I might be way off though only he knows if he intimidated. Hill on KC although he's small too he seem so much tougher and stronger. There were a lot of small receivers that are just so tough to defend so there no reason why Brown with all his talent can't be as well. Look at Welker, Edelman, Largent and so on.