It could be related to Sasuke. If Sakura thought Naruto was endangering Sasuke in some way, or if Naruto thought Sakura was being too naive about Sasuke's actions, it could lead to a fight. Their feelings towards Sasuke have always been a complex and important part of their relationship, and any differences in how they handle Sasuke - related issues could spark conflict.
Perhaps it's a training exercise that gets out of hand. In the world of Naruto, intense training often mimics real battles. If they were sparring and emotions ran high, it could turn into a full - fledged fight. Also, Sakura might be trying to prove herself to Naruto, and Naruto, not understanding her intentions, might respond aggressively.