I have a 12 y/o gelding that we have had since the middle of February. He has been kind and gentle. He is green broke but thus far has been very willing to learn. We have been for several rides and he has done well. He stands quietly for grooming, saddling, or just stand tied. He stands to be mounted. He is not aggressive with his food. He trailers well. He has not once offered to kick. He did grab my shirt sleeve with his lips once while I was leading him. He is nonaggressive out in the pasture with the other horses. He has had someone that has gotten after him on his hip with the reins while riding. Apparently he would do no more than walk while being ridden. I have been able to get him to successfully walk, trot, and canter under saddle. Well, today I decided that I would try to lunge him to help build some muscle, etc. Anyways, I had a feeling this would be entirely new to him and expected to have to deal with confusion getting him to move forward, maybe even trying to run out straight, etc. I was totally unprepared for what he did do. He was not afraid of the whip. As soon as I got him a bit away from me he turned, pinned his ears back and charged me. Needless to say this was frightening. I tried my best to hold my ground. The higher I raised my hands to get him to stop the higher his front feet came off the ground as though to rear and strike me. I got him settled down and tried again. Same result. He would stop when I put my hands on his shoulders but still ready to charge me again. I am not in a round pen, this is on the ground with a lunge line and a lunge whip. He would charge right up, teeth barred, small rears, ears pinned, very aggressive as a warning. He never did strike or bite. We did this several times. I got him to settle and worked him leading, walk and halt, back, turn, etc. Then I worked with him asking him to move from pressure, not much response on his poll, slow response on shoulder, and great response on hips. Then I got him to walk around me, very short lead, and the whip as a visual behind. He did okay but the further back I got on his shoulder the more his ears would go down. What I am looking for are some ideas of what to do. Thanks in advance.