This is a vintage Happy House Darts shirt, it is in excellent condition and labeled as a size XL. Measurements below:
pit to pit: 23"
length: 29"
Happy House Darts appears to be an organization that runs dart leagues and tournaments, including events at various locations such as Elks lodges. "OU812" might be a specific team, event, or reference related to the league. "Elks Rochester" likely refers to a local Elks Lodge in Rochester that hosts dart competitions.
For more details about upcoming leagues and registration, you can check their official website: Happy House Darts.