If you're into sports, you've seen it happen. You've probably even experienced it: Football players shaking hands after four quarters of knocking each other around. Tennis players leaping over the net to shake hands with their opponents after a hard-fought match.

Soccer players exchanging jerseys after an intense 90 minutes. Even boxers touching gloves at the beginning of each round, then hugging each other after beating each other into a pulp for 12 rounds.