"You're cheating! You can't move the knight there! That's illegal!" Sherlock took a threatening step forward to the edge of the board. Never mind that there were children around; that bastard had just cheated! Rolling up his sleeves, he quickly strode around the board and threw a punch at his opponent.
He managed to get in a good right hook to Jim's jaw before getting hit himself. Cursing, he stumbled back and wiped the blood off his chin with the back of his hand, then began kicking over the pieces within his reach. Jim growled and stormed off, leaving Sherlock to finish his childish rampage to knock over all the pieces on the board.
"Mummy won't be pleased to hear you had a juvenile scuffle with that Moriarty boy," A voice chided from behind him.
"Shut up, Mycroft," Sherlock snarled as he finally finished by smacking the black queen onto her side, not bothering to turn around. Mycroft raised his eyebrows and twirled his umbrella absently, moving into the room.
"You know, there are more ways to prove superiority than a fist fight." Mycroft placed his free hand on Sherlock's shoulder.
"We were playing chess, I was winning, so he decided to cheat. That's all." Shrugging off Mycroft's hand, Sherlock stalked off towards the exit. The elder Holmes watched him leave, shaking his head as he returned to the library.