赛事 (sài shì) is a formal noun for a competition, especially a large sporting event or series of events (e.g., 奥运赛事 'Olympic events'). It is more specific to organized tournaments than 比赛 (bǐ sài), which is the everyday word for any match or contest and can also be a verb. 大赛 (dà sài) refers to a grand-scale contest, but 赛事 emphasizes the scheduled event itself.