This horse has an unhappy mouth, indicated by opening the mouth against the bit and the head tossing and tipping at odd angles.
It can be called by several different names: fighting the bit, fighting the hand, resisting the hand, resisting the contact. All of it means a problem for the horse, and he is trying to communicate that to the rider.
It could be a problem with the bit not fitting, the mechanics of the bit not appropriate for the job, the noseband interfering, or the heavy contact.
In addition to the video below, how about the horses in these videos: