Complex sentence: He rushed for a Steelers single season record 1,690 yards and also broke Franco Harris'team record for 100-yard games in a season with 12, that also tied Eric Dickerson's NFL record for 100-yard games.
Split into simpler sentences: He rushed for a Steelers single season record 1690 yards and also broke Franco Harris'record for 100-yard games in a season with 12. That tied Eric Dickerson's NFL record for 100-yard games.