Fantasy Baseball Forecaster for Week 21: Aug. 28-Sept. 3

Bryan Woo of the Seattle Mariners. Jamie Sabau/Getty Images

September arrives during fantasy baseball's Week 21, on Friday to be exact, and with it another important stage on the baseball calendar.

Thursday, Aug. 31, represents the final day for a player to become contracted to a major league organization and be eligible for the postseason roster. Non-waiver trades -- in other words, trades involving anyone on a team's 40-man roster or 60-day injured list -- are no longer allowed after the Aug. 1 trade deadline in the current labor agreement, but trades involving players outside that pool are. This is how a trade like the one the Oakland Athletics and San Francisco Giants made on Monday, involving Sean Newcomb (going to the Athletics) and Trenton Brooks (going to the Giants), occurred, as neither player was on a 40-man roster. It also means that teams hoping to sign players, even for depth purposes at the minor league level, such as the Cincinnati Reds' signing of Trey Mancini on Wednesday, need to do so by Thursday to earn postseason eligibility.

Friday, Sept. 1, is the day that major league rosters expand from 26 to 28 players, including a 14-pitcher cap. You can count on there being another 60 players activated to rosters by teams on that date, which could influence teams' rotations, lineups or pitching plans. It might also be a day where we see a handful more top prospects recalled, such as any of the five I wrote about Wednesday.

There is one make-up game during Week 21, as the Chicago Cubs and Cincinnati Reds will play a doubleheader on Friday at Great American Ball Park, with one of the games rescheduling their April 5 postponement. Each team will play seven games as a result, the Cubs and Reds among the nine teams scheduled for seven contests in the week.