It's Hot Stove League time and Jimmy Fallon pays tribute to the classic Abbott & Costello routine "Who's On First" (whether there is a question mark depends if you're looking at it from Abbott or Costello's point of view - I prefer it without since it's a statement of fact), and, in the process introduces some of the players, portrayed by Billy Crystal and Jerry Seinfeld, into the skit. The St Louis Wolves uniform was what Bud Abbott wore in the 1945 film Naughty Nineties in which he and Lou Costello performed the routine.
Bud and Lou developed the skit during the 1930s and performed it thousands of times (usually with some variation). In 1999, Time named Who's On First the best comedy sketch of the 20th century. Here they are performing it on TV in the 1950s. Jimmy Fallon has a great talent for doing well-done tributes to comedy and music acts. From a prior post here is his send up of The Doors: This Is The End (Of Reading Rainbow).