Aggressive 2 year old please help :(

[Mrshrb1988]

I have a little boy who is two years and 9months old. he's a lovely little boy most of the time but can be aggressive with other children. He has one "friend" in particular who is 3 months older and he really struggles with him everytime he comes over my little boy is trying to snatch everything and saying it's mine! he is very prone to pushing this little boy also this little boy is very loud and bossy at times and will get in my little boys face and this causes my son to push him or hit him (not very hard but still) and then if he's sitting in his pushchair this little boy will run toys up and down my sins arm and even this will cause him to be aggressive and try and hit out or kick out. He isn't anywhere near as bad when we go to playgroups and he went to a birthday party the other night and he was much better no hitting or anything. But today at the school playground the little boy sat in his pushchair had biscuits he had made at nursery and was if I'm honest teasing my little boy but my little boy kept trying to snatch the biscuits and then attempted to kick him I just don't know what to do ladies please a bit of advice :( sometimes he can share lovely like with his baby sister and other times he's horrendous. :( Is it his age is this "normal"