J.M.
S.,
All of my children went through that phase one way or another. I had a couple that slapped and one that head butted...that one was awful. How we dealt with it was to tell the baby no (firmly) while holding the hand that they hit with, and then put the baby in their play pen or crib without a bottle or toys. I don't mean keep the baby there for a long time, but just like time out with older kids, a minute for 1 year old, 2 minutes for 2 years old, etc. Although it may not seem long, they do understand after a few times. No baby wants mommy to put them down. It should correct the issue pretty quick. Hope this helps!
J.