S.H.
As all the others said, it is NORMAL. Also, at this age and stage... most children "parallel play." So bear in mind your son's age and development. Don't put adult expectations on him, as you would expect an adult or older child to behave. Children are just learning about their world now. Children this age don't have social skills per say yet, they are just learning about things in relation to their development. So to expect a 1 year old to "play" with a friend in a cooperative way, may not happen. In fact, through out their entire toddler-hood & early childhood, they are just learning about "social skills" and cooperative play. At this age, "knowing" about how to act "gentle" and empathetically and to "share".. is abstract for them. Their cognitive development for this is not aligned yet. But, sure, introduce examples and words for feelings. Also, from this age up, their world is "me" centered... and like physical development... a child/baby is STILL developing "feelings" and may not know how to express it yet. It's all about "ages & stages."
Perhaps, get a book on it. The book "What To Expect The First Year" by Arlene Eisenberg is good. Or read up online about developmental stages per each age.
Some children this age not only hit, they bite too or pinch. It's all normal stages of development. It's best to redirect their behavior or distract them.
Here are links about parallel play"
http://wondertime.go.com/learning/article/baby-parallel-p...
http://www.netwellness.org/question.cfm/11700.htm
http://pediatrics.about.com/od/growthanddevelopment/ig/De...
http://www.kidshealth.org/parent/growth/learning/learn12y...
http://parenting.ivillage.com/tp/tpdevelopment/0,,devtrkr...
Good luck, hope this helps,
~Susan
www.cafepress.com/littlegoogoo