ditto on the language/expressing himself if it is hitting when he's angry. Our son's hitting was part of his tantrums.
DS is an intense child and though he has fantastic language skills, he gets extremely overwhelmed with his emotions when he gets really frustrated. He trembles and shakes, stutters, flaps his hands, yells, cries, etc. till he can get himself under control. Around 2.5ish years, till about 6 months ago (he's almost 4 now) he was hitting me. Hard. If I knelt down to talk to him, he'd slap my face. If I held his hands, he would head butt my nose like a street fighter. (obviously, I should say, this is NOT a behavior he has EVER seen) He also was kicking, etc.
Because he was totally out of control, a time out didn't really help him, but I would often have to put him in his room and hold the door shut for my own sanity. I also found that if I avoided kneeling in front of him, and stood up, the blows would go to my legs, which was less painful, so helped me stay calm longer...
However, if and help him talk his way through the emotions, he does better. I gently hold his hands in front of him, coach him through taking deep breaths, give him a script to repeat after me "I feel angry... etc." , he does better. He just needed to figure out how to ride that emotion wave. Now that he is internalizing that script, he often takes the deep breaths himself, and though he still gets angry/frustrated, he has more strategies to deal with it, so he is outgrowing the more violent expressions.
Because he IS very articulate, there was a hilarious phase when he would describe, in elaborate detail, what he was going to do, for example: 'Mommy, I am going to hit you in the face, and put you outside, and you will be cold, and you will not like, it, and you will be sad.' (again, NOT something we EVER do/threaten.) It was hard not to laugh. The new script is more effective, but not as funny,.