Wiktionary
fantasy baseball
n. A competition in which participants select combinations of baseball players in a real league and score points according to their performance.
Wikipedia
Fantasy baseball
Fantasy baseball is a game in which people manage rosters of league baseball players, either online on in a physical location. The participants compete against one another using those players' real life statistics to score points.
Usage examples of "fantasy baseball".
None of these kids are going to spend the off-season playing fantasy baseball in Florida with overweight businessmen, or signing expensive baseball cards at memorabilia shows, or touring the chicken circuit at two thousand bucks a night.