Complex sentence: While attending a Chicago baseball game as a spectator one Sunday, O'Day was recruited from the stands to substitute for umpire Thomas Lynch (the future NL president), who was unable to make it to the game due to a train service cancellation.
Split into simpler sentences: While attending a Chicago baseball game as a spectator one Sunday, O'Day was recruited from the stands to substitute for umpire Thomas Lynch. Lynch, who later became the NL president, was unable to make it to the game due to a train service cancellation.