Draft/TB cross won't move forward under saddle. Bucks when I use crop. Any ideas?

I just bought a 6 yr old Percheron/TB cross. He was just broken about a year ago. When I went to try him he was great w/t/c on lounge line, walk trot under saddle no problem. he has been at my place now a week and when I rode him the other day he would not go forward. He planted his feet and pinned his ears. I used the crop on him and he bucked. Not really sure what the problem is? I am pretty certain his saddle fits fine and I am using a full cheek snaffle bit. Any suggestions??