No, Yahoo is not responsible for stepping in on league disputes. That falls solely on the league commissioner.
Depending on the league, either the commissioner can Veto the trade, or the league can vote for a veto. Find out which one it is by clicking on the pending trade, it will either say "Vote against this trade", or "contact commissioner about this trade" or something like that.
THe best you can do is either vote against it, or voice your concern to the commish and the rest of the league.
That is a pretty bad trade, and obviously deserves to be veto'd.
If it isn't resolved, I would suggest just quiting. Tell the commish to find someone else to take over your roster, or just don't set your roster at all and forget about the league.
This is what you get for joining public leagues. They are horrible. Next time just try to find a private league to join, many less problems like this, because most of the managers actually care about it.
Last, if you really feel scorned over the whole thing, drop as many of your good players as you can (the ones that are not on the can't cut list) and add the lowest ranked players to your roster. This will really mess up the whole league lol... I would NEVER recommend doing this in a respectable, competitive league. But Public leagues where trades like this go thru with no complaints are not worth your time.
