Once upon a time, major league baseball teams had to give up major league players, from what was called a "compensation pool", if they signed a free agent under certain conditions; free agents were separated into Type A (major league compensation), Type B (draft pick compensation) and Type C (no compensation).
A number of players swapped teams under this early-1980s scheme, most notably future Hall of Famer Tom Seaver, who had been left unprotected by the Mets, who thought his big contract would prevent him from being selected. Mets fans were horrified, and Seaver wound up posting his 300th career win in the red-white-and-blue White Sox uniform of that era instead of Mets pinstripes.
There are more details on this short-lived system here; it met its demise after the Yankees lost just-drafted Tim Belcher to the Athletics (because he had been signed too late to exclude him from the compensation pool), to the consternation of George Steinbrenner, who led the move to eliminate the system in the next CBA. No one had really liked this system in the first place, and it was replaced by a system where teams got draft picks, based on a ranking of free agents, this time "Type A" and "Type B".
Over time, teams began gaming the system, to the point where certain clubs were able to stockpile draft choices. Harrumphing loudly, the Powers That Be declared that this system must be changed, and so it has been; no more "Type A" and "Type B" free agents; only players who get high-dollar offers will rate compensation.
That seems all well and good, but there might be one provision that will result in unintended consequences:
If a player gets traded in midseason, the team that trades for him will get zero compensation, no matter how big a star he is. Doesn't matter if he's CC Sabathia or Felipe Lopez. The only players who can bring any sort of compensation are players who spent the entire season with one club. Think that'll change the July trade-deadline madness? Teams are still trying to figure that out themselves.
It very well could change the "July trade-deadline madness". Do you think the Pirates would have dealt for Derrek Lee this past summer if they knew they wouldn't get compensation if he left? The Pirates did offer Lee arbitration under the old system, but it doesn't seem likely that they would under the new, and maybe they wouldn't have traded for him at all.
In trying to eliminate a system that some felt was being unfairly leveraged, baseball moguls could have thrown a wet blanket over July trades. We won't know for sure until next summer.
There's another unintended consequence that could occur in 2013 when the Astros move to the American League; with 15 teams in each league it will be necessary to have interleague play all season, instead of having it shoved into one block in June. Maury Brown points out a potential issue:
Imagine the Red Sox are fighting for a playoff spot, and instead of playing games in division where they can quickly climb up the standings, they have to hop a plane and play the Reds. Suddenly, there’s no DH and your pitcher is a critical player in your offensive line-up.
That's not just a plausible scenario, it very likely will happen. You're thinking, "What's the big deal? Just make sure contending teams don't have to play interleague games in September."
That sounds easy in principle, but doing it in real life might not be so simple. For one thing, no one yet knows what the breakdown of games must be for such a schedule to work. Baseball's schedulers might be able to work out a scheme where no one plays more than 18 interleague games (the current maximum), but another workable schedule would have teams playing as many as 30. It just doesn't seem possible to avoid one or more AL contenders missing their DH when they most need him; even if you try to schedule, say, only the "worst" teams from the previous season into September interleague games, what happens if an AL team not expected to contend has a miracle season?
The obvious answer is to have the DH in all games -- especially if there are 30 interleague games, where you'd force the AL club to play without its DH in 15 road games, almost 19 percent of its road schedule. Or get rid of it entirely. The leagues are no longer separate; there are no longer individual league presidents and they share umpiring crews. They're more like the NFC and AFC than the bitter rivals they once were.
Regardless, there are going to be consequences from the new CBA that no one anticipates, even with so many words being spilled over the last few days about how "awful" the new draft caps are. Baseball people are resilient and resourceful. Those who figure out how to leverage the new system will wind up winners; others will scramble.
The only thing we do know for sure is that over the five-year span of the agreement, things will be revealed -- the above are just a couple of examples -- that we can't possibly know now.