If a professional athlete - golfer or baseball player - receives pension benefits from the PGA or from MLB, are those benefits subject to United States income tax? If so, would only a portion of the benefits be taxable - the portion attributable to work performed in the United States? So for example if a MLB player from Japan plays for the Yankees, who travel to Toronto several times a year, is that portion exempt from U.S. taxation? Or a golfer from South Africa who plays tournaments all over the world - does he pay U.S. tax on his pension? Just on the portion attributable to service in the Unitted States, or no U.S. tax at all?

Thanks