Sunday isn't just the day when the calendar turns to the final month of the regular season. It's also when teams have the opportunity to expand their rosters.
Starting on Sept. 1, Major League rosters can increase to 40 players for the remainder of the season. The reasons to call up players are plentiful. Some teams will hope they will provide a boost to a playoff push, while others will be giving future impact players early auditions in order to see what they can do.
Variables can come into play when roster-expansion decisions are made. One is roster space. A player must be on the 40-man roster to get a September callup. If he's not on it, space must be made on that roster so that he can be added to it. But teams aren't always willing to add some players, especially if they don't yet have to be on the 40-man in order to be protected from the December Rule 5 Draft.
That leads to variable No. 2: need. A playoff contender will only ask for a farm-system boost if there's a call for one, and teams out of contention aren't likely to bring up a top prospect if there isn't an opportunity for them to get playing time.
Other things that might be considered: Where a player is in his development and whether his Minor League team is in the postseason. Case in point: Don't look for the Angels to make any huge callup waves, because both their Triple-A and Double-A clubs appear to be playoff bound.
Jameson Taillon of the Pirates is a prime example of the individual plan perhaps not matching heightened expectations. The big right-hander, ranked No. 10 on MLB.com's Top 100 Prospects list (and No. 1 on Pittsburgh's Top 20), was moved up to Triple-A at the beginning of August, leading many Bucs fans to wonder if perhaps the 2010 first-rounder could be in line to join the big club, maybe in a David Price-like bullpen stint, in September. But that's not going to happen. The plan all along was for Taillon to get some Triple-A time late in 2013, so Pirates fans will have to wait until 2014 to see him pitch in PNC Park.
Some top prospects have already been recalled. Xander Bogaerts, No. 6 on the Top 100, was added to Boston's active roster on Aug. 18. The Mariners' Taijuan Walker (No. 4 overall) is to make his Major League debut this weekend. Orioles top prospect Kevin Gausman (No. 14 overall) and Rays No. 2 prospect Jake Odorizzi (No. 40) were both brought up this week. As a result, both will be eligible for the postseason, though September callups can be added to replace players on the disabled list.
In addition, the Red Sox could easily bring up reinforcements behind Bogaerts. Jackie Bradley Jr. and Allen Webster -- the Nos. 2 and 3 prospects in the organization -- are Top 100 guys who have seen big league time this year and might be in the September picture. Anthony Ranaudo and Garin Cecchini, Nos. 82 and 85 in the Top 100, would have to be added to the 40-man roster, but both are having some success in Triple-A.
Other Top 100 players who could potentially help out contenders include Nick Castellanos of the Tigers (No. 11) and Billy Hamilton of the Reds (No. 17). While space would have to be cleared on Cincinnati's 40-man roster for Hamilton, his plus-plus tool -- speed -- could really make an impact in the National League Central. Also in that division, the Cardinals have already brought Michael Wacha (No. 16) back up and Carlos Martinez, who recently graduated off the prospect list because of service time, could also return to provide pitching depth.
And what about a few more outfielders creating some excitement for both contending and non-contending teams? The Dodgers considered bringing up Joc Pederson earlier in the year, but opted for Yasiel Puig. Could the No. 45 overall prospect be brought up from Double-A to help now? In Oakland, the A's are likely discussing whether Michael Choice, their 2010 first-round pick who is the No. 93-ranked prospect, can help their playoff push in the American League West.
On the other side of the spectrum, Astros fans have been clamoring to get a look-see at George Springer (No. 24), who is just three home runs short of an astounding 40-40 season in the Minors.
Other Top 100 players who could make September interesting for teams out of the race include Yordano Ventura of the Royals, Marcus Stroman of the Blue Jays and Archie Bradley of the Diamondbacks. There's no indication any of these exciting pitchers will get the call, but it sure would be fun to see them make their Major League debuts.
Jonathan Mayo is a reporter for MLB.com and writes a blog, B3. Follow @JonathanMayoB3 on Twitter.