The 2010 series allowed each team to make use of a 19 @-@ man active roster . Exceptions were made in two cases that allowed teams ' active rosters to expand to 21 players , both times for the same reason . Two games during the season had to be postponed because of poor weather . Both games involved teams meeting for the first time during the season ; make @-@ up games were scheduled at the start of the return series between the teams , and this resulted in two four @-@ game series . In both cases , the teams had a 19 @-@ man roster for the make @-@ up game , and an expanded 21 @-@ man roster for the originally scheduled series .