What makes a player eligible?
Players are divided into two groups determined by age on draft day. The first group is any player 18 years or younger on draft day that has spent five years in the minors without being added to the 40 man roster is eligible to be taken in the draft. This year that means international free agents (July 2 signing period prospects) and high school draftees from 2010 are eligible. The second group is any player 19 years or older on draft day that has spent four years in the minors without being added to the 40 man roster. This year that's any junior college or four year university player that was drafted in 2011 and not added to the 40 man. Of course, anyone drafted/signed before the newly eligible players are also still eligible to be drafted.
What goes into drafting one of these prospects?
A team that drafts a prospect has to pay $50,000 to the team that the prospect was drafted away from. The drafting team also has to keep the prospect on their roster for the whole season. The player can be claimed by or traded to another team, but can't be sent back to the minors without being offered to his original team first. Nate Freiman was selected by the Astros but placed on waivers. He was then claimed by the A's who gave him a spot for the whole season; however, if he had made it through waivers he would have had to be offered back to the Padres whose system the Astros drafted Nate out of. If the team returns the drafted player, then the original team pays $25,000 for the player. Basically it costs nothing monetarily to draft a player. A team can pass if they want to, last year only 9 teams actually took a player during the major league portion of the draft: The A's were not one of those teams.
Oddly, those rules don't apply to the minor league (AAA and AA) portions of the rule 5 draft. If a player is selected in those portions, it doesn't matter if he's promoted or demoted, he's now property of the drafting team. There's a cost to drafting a player, but it's less than half of the major league phase of the draft.
Who are some candidates for the A's to protect?
The obvious name that the A's should protect is Renato Nunez, a top 6 prospect in the A's system. The power hitting third baseman out of Venezuela was signed to a $2.2 million bonus in 2010. He had a very good year in Stockton to the tune of an 853 OPS and will be in Midland next year. A team may be willing to give him some time in a role similar to Freiman. He needs work on his approach:113 strikouts to only 34 walks in 563 plate appearances, although both trended in the right direction from 2013 in a similar amount of plate appearances.
Seth Frankoff got off to a slow start in the A's system as a starter but took off once he became a reliever, climbing three levels in two years. He doesn't have plus stuff: A solid breaking ball and a fastball that sits around 90. On the other hand he has solid control and does get swings and misses. After his midseason promotion from Midland, where he had put up career best numbers, he struggled in AAA in roughly 30 innings. That could just be small sample size noise in a hitter friendly league, but whatever the reason it may be a deterrent from adding him to the 40-man roster. He'll be 26 all of next season.
Ryan Doolittle's career has been fairly injury plagued, not unlike his older brother's career as a hitter. He can run his fastball up to 94, although he's generally in the 88-91 range. 2014 was his first fully healthy season coming off of TJS. Doolittle spent most of his year in AA where he had some trouble with command (3.6 walks per nine) but went to the Arizona Fall League where he didn't walk anybody in 13 innings and struck out 11 batters. He will be 27 all of next season.
Tanner Peters had a breakout season in 2013 in Stockton as a starter, but was plagued with injuries this year in Midland. He mustered only 27 innings this year including a stint in the Arizona Fall League. In 2013 Peters had exceptional control, including flirting with a no hitter on a couple occasions. There isn't much reason to think his control has gone, either. His fastball is average at best, but his changeup is solid and he has a breaking ball as well. If the A's don't, another team may think he's still able to start, but he could provide a middle inning reliever if a starter can't make it deep into a game.
Josh Whitaker is the only position player from the 2010 or 2011 drafts still with the A's to make it past AA in a starting capacity, but injuries slowed him down this year. He started out repeating AA and got off to a hot hot start, OPSing .890 in 215 plate appearances. He was promoted to Sacramento midseason and displayed more of his power (his best tool) but never got a chance to raise his walks or his batting average enough to supplement the power because he was injured after just 22 games. The injuries may make other teams wary of using a roster spot on him, but a team that played in AA against him might be interested in what tools he could show in a bench role as an OF/1B. He can also steal a base or two.
Other names of eligible players that some of us may be aware of are Aaron Shipman, Bay Area native Chris Lamb, and Drew Granier.
Trades by various teams will be made to make room for some of their eligible prospects, so that will be something to watch for as well.