Aggressive

To be aggressive one must be assertive to the point of being willing and able to do harm to the target of aggression in order to achieve a goal.

For instance, the football player was so aggressive in the game that he frightened some members of the opposing team. There are many identified sources of aggression; instrumental, frustration, retaliation, expressor, relational, progressive, impulsive, reactive and hostile. Each of these has its own triggers and its own reason for existing.