You've got one minute to get in as many pull-ups (in good form) as possible using a pronated or overhand grip. You can take breaks, let go of the bar, or call your mom and tell her you won't be home for supper... just as long as your chin gets above the bar on every rep.
This challenge can be as much about strategy as it is about measuring your testicular fortitude, so have a plan. Hit your reps in spurts and rest before the burn takes over. That way you can stay fresh for the first 50 seconds. At the 10-second warning, turn it on and go for broke, hitting as many reps as possible.
Your goal is to get at least 25 reps, and anything over 30 reps is noteworthy.