Yes, your best friend may become your worst enemy! At least in the sport of arm wrestling.
Arm wresting is a unique and great sport because during a match, your best friend will become your worst enemy and vice versa. To clarify, this is only in a competative sense, however, it must be this way if you want to be a champion. When I am at a competition, I socialise, am friends, and I chat with almost all the competitors. I talk to their friends and families, as well.
Competitions are very enjoyable and a great place to make new friends, chat and joke around. I have found that arm wrestlers are good people with a variety of backgrounds and training regiments.
What I have found is that things stay relaxed and social until they call your name and you are on deck to compete. All the people at the event are your friends but when the call your name and your opponents, your best friend becomes your worst enemy.
Just prior to competing, I go into competition mode and will do all I can to win. Friendship takes a back seat.
This only happens for a short time until the match is complete, and then your worst enemy goes back to being a friend.