Having a problem with my male cat

I am not certain what started this behavior, I have 4 cats three females that are spayed one male that is not fixed, I take my cats out into yard and stay with them due to living on two busy intersections so they can get some fresh air, My male  cat is extremely very territorial about other cats coming on the property and he has gotten into scraps before, This problem with my male cat started about a week ago, one got into a fight with a young grey  tabby in the yard and U broke it up, The next day or so latter for not reason he started a major fight with his sister who is also a grey tabby, this has happen one or twice with the other females, But  each time I take them out he waits his chance to right after his sister again, and he will not stop, I know have to stay between them every time I take them out, usually they get along fine, also this only happens when I take them out side once they are inside they are fine, I was thinking for some reason he may be confusing his sister with the other cat cause they are close to the same size and are both grey tabbys, But this does not make much sense seeing it only goes on when they go out side, anyone got a clue what might be going on ?

Methen said:

 
I am not certain what started this behavior, I have 4 cats three females that are spayed one male that is not fixed, I take my cats out into yard and stay with them due to living on two busy intersections so they can get some fresh air, My male  cat is extremely very territorial about other cats coming on the property and he has gotten into scraps before, This problem with my male cat started about a week ago, one got into a fight with a young grey  tabby in the yard and U broke it up, The next day or so latter for not reason he started a major fight with his sister who is also a grey tabby, this has happen one or twice with the other females, But  each time I take them out he waits his chance to right after his sister again, and he will not stop, I know have to stay between them every time I take them out, usually they get along fine, also this only happens when I take them out side once they are inside they are fine, I was thinking for some reason he may be confusing his sister with the other cat cause they are close to the same size and are both grey tabbys, But this does not make much sense seeing it only goes on when they go out side, anyone got a clue what might be going on ?

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Edit for typos:

I am not certain what started this behavior, I have 4 cats three females that are spayed and one male that is not fixed, I take my cats out into yard and stay with them due to living on two busy intersections so they can get some fresh air, my male  cat is extremely very territorial about other cats coming on the property and he has gotten into scraps before, This problem with my male cat started about a week ago, He got into a fight with a young grey  tabby in the yard and I broke it up, The next day or so latter for not reason he started a major fight with his sister who is also a grey tabby,Tthis has happen one or twice with the other females, But  each time I take them out he waits his chance to go right after his sister again, and he will not stop, I now have to stay between them every time I take them out, usually they get along fine, also this only happens when I take them out side once they are inside they are fine, I was thinking for some reason he may be confusing his sister with the other cat cause they are close to the same size and are both grey tabbys, But this does not make much sense seeing it only goes on when they go out side, anyone got a clue what might be going on ?

Since no one has replied I will. The problem is, simply put, that he is intact. That causes all sorts of territorial and behavior issues. Any reason why he isn't neutered yet? That will solve a load of problems. Remember it will take time for the hormones to leave his system once neutered but that is the best answer for you.