Clippard, 23, was 6-13 with a 4.66 ERA in 27 starts with Columbus. Clippard struck out 10 batters in his final start of the season on Sunday vs. Toledo. Clippard also went 1-1 with a 4.35 ERA in two starts for the Nationals.
O'Connor, 28, went 5-3 with a 2.14 ERA in 17 starts for Columbus and the Gulf Coast League Nationals. He also pitched in five games for Washington and had a 13.00 ERA.
Wagner, 26, pitched with Columbus and Class A Potomac and went a combined 0-3 with a 4.44 ERA in 23 games.
Maxwell, 24, hit .233 with seven home runs and 28 RBIs in 2008 in 43 games. Maxwell posted 31 walks in 43 games en route to posting a .367 on-base percentage. He also scored 35 runs.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.