I've never had a good experience with individual metrics leaderboards. On one team we had a JIRA story point tracker shown on a tv by a clueless exec. Devs did everything they could to game the system and tasks that required uncertainty (hard tasks) went undone. I believe it contributed to the cog culture that caused an exodus of developers.

However, I love the idea of an occasional team based leaderboard for an event. I've held bug and security hackathons with teams of 3-5 and have had no problem with them.