The AFL is players that the organization is pushing.
The Arizona Fall League is baseball's way of extending the minor league season for a handful of prospects from each MLB club. The league forms rosters of teams with eight players from five major league teams. The six teams then play each other during October and November.
In the past, Mike Trout played Winter Ball (and had a terrible AFL season) and was teammates on the Scottsdale Scorpions with Bryce Harper. Years ago Chone Figgins refused an assignment to Winter Ball but nevertheless rose thru the organization. This year the Angels make up part of the Mesa Solar Sox. The four other teams adding players to the MSS are the Nationals, Blue Jays, Cubs and Athletics.
The Future Halos making this year are:
Trevor Gott (AA, Halos Heaven Rank: 14)
Dan Reynolds (AA, Halos Heaven Rank: 26)
Mark Sappington (High A)
Nate Smith (AA)
Stamets is on the restricted list and can only play in games on Wednesday and Sunday. 66ers pitching coach and former Angel starting pitcher Matt Wise will be part of the Mesa coaching staff.
Inclusion in the AFL is not an indication of a prospect's status. A lot of players are "on the bubble" and the organization may want to watch them a little more carefully before cutting ties with them. Many players are given definite instruction on what to work on in the AFL, be it pull hitting or throwing a certain pitch. If a player tears up the AFL you will see their national rankings on prospect lists go up but if they tank they often get a free pass for just being too damn tired at season's end to produce.
On the field, players wear their AFL team's cap but put on the jersey for the team with whom they are signed. MLB estimated that sixty percent of AFL players eventually play in the Major Leagues.