Complex sentence: Buescher made his Sprint Cup Series debut in the No.34 Ford for Front Row Motorsports at Fontana, filling in for David Ragan, who had been filling in for Kyle Busch, who had been out for a fractured leg.
Split into simpler sentences: Buescher made his Sprint Cup Series debut in the No.34 Ford for Front Row Motorsports at Fontana. He was filling in for David Ragan who has been filling in for Kyle Busch who's been out for a fractured leg.