James G, --- True, we assume all sorts of risks, all the time. Oversimplifying things (not because of my opinion of you or anyone else here, but because law has a way of making things tedious and complicated), tort liability occurs when someone is injured due to another person's negligence.
"Negligence" can be generally defined as not doing what you reasonably should have done to prevent the accident in question. That standard varies with circumstances. I would not presume to predict how a suit over COVID-19 exposure would play out--much would depend on the facts and the laws in the relevant state. But a plaintiff could potentially argue that by holding a tournament, an organizer represented that they took reasonable precautions against COVID. If there were a cluster of infections traced to the tournament, then maybe the precautions weren't so reasonable. (Google "res ipsa loquitur" if you want to go further down the doctrinal rabbit hole.) Perhaps there should have been more sanitizing stations, fewer spectators, better screening of players who showed symptoms... And maybe most important of all, if a claim is plausible enough to survive a motion to dismiss (early in the lawsuit, before things get really expensive), then a defendant may pay a settlement just to avoid the costs of litigation and the risk they will owe even more.
I'm not a plaintiffs' tort lawyer and I'm not defending the system. There might never be a suit filed, or a court might toss a suit because of a waiver (or maybe not). Lots of other outcomes are possible, too. How serious is the risk? You'd have to ask your lawyer to give you an answer specific to your situation.