A gentleman's agreement is an informal type of eligibility rule that has been used for events like the Early Fall Tournament and ACF Fall. Instead of explicitly barring people based on experience or educational progress, individuals are encouraged to personally evaluate whether they are the appropriate audience for a tournament.
For example, a second-year grad student who is usually a 15 PPG player and is unlikely to massacre the field by themselves may find ACF Fall an appropriate tournament to play, but a first-year who is a star player and could dominate the competition may not.
The implementation of this policy has been mixed, with some people who clearly are not the target audience of these events playing them anyway. However, it still offers some advantage over the more inflexible rules for participation in other "novice tournaments," which may bar upperclassmen or graduate students who are in fact "novices" at quizbowl.