Conversation so far:
When did Welch join Fleetwood Mac?
1971, when he was invited to join Fleetwood Mac.
What was his role with Fleetwood Mac?
Welch helped to steer the band in a more melodic direction, particularly after lead guitarist/singer-songwriter Danny Kirwan was fired.
Was Welch successful?
In September 1971, the band released Future Games, with the title song written by Welch.

Question: What was the song?
Self-contained rewrite: What was the title song of Fleetwood Mac's Furute Games?