Complex sentence: Jackson's knees prevented him from appearing in many games with Jersey City as a player, but he remained as the team's manager until July 1938, when he was replaced with Hank DeBerry.
Split into simpler sentences: Jackson's knees prevented him from appearing in many games with Jersey City as a player. Jackson remained as the team's manager until July 1938, when he was replaced in Jersey City with Hank DeBerry.