Malice (or lack thereof) is not a factor, so don't focus on that. However, there are several other reasons to think that you are not liable; while no lawyer can guaranty that you would not lose if sued (every lawyer has seen courts and judges do odd things and make bad decisions), you appear to have a good defense to liability:1) Most fundamentally, you are only liable if you were "unreasonably careless," with unreasonably careless being judged contextually. If you were not being wilder or more violent than other people in this class, were not attacking someone when you were not supposed to (e.g. before "action" or "start" or whatever was called), then you were most likely not being unreasonably careless. An accident by itself does not equal liability; there must be a lack of appropriate care for that situation. So if you were doing what you were supposed to the class, there is no reason to think you were unreasonably careless.2) Almost as fundamental and also in your favor: assumption of the risk. Certain activities are inherently riskier than others; when people voluntarily do them, they "assume"--or accept--the normal risks attendent upon those activities and can't sue for them. Example:  people fall while skiing and sometimes they break a leg or get a concussion. If that happens to you, you can't sue the ski slope. In this case, if you engage in sparring or stunt fighting, the possibility of a blow landing is a normal risk; by voluntarily participating in the class, the other person assumed this risk and cannot recover compensation when it occurs.