I know: there's just no way I can hope to get people from speculating about a convention in which no candidate enters with 50% plus one of the delegates. And, you know, there's nothing theoretically impossible about it. It could have happened in 1984, if Jesse Jackson had been a bit stronger. It's possible to imagine a left-libertarian candidate running on a platform similar to Gary Johnson's managing to force it in 2008 on the Democratic side. There's good reason why it doesn't happen (the logic of winnowing), and I'm confident that it won't happen this time, but it could.
But please: if you want to speculate about this (and I'm looking at you, Nate Silver), please, please, call it a deadlocked convention. Not a brokered convention. One more time: there are no brokers. Delegates are generally slated by the candidates, and while they are likely to be loyal to those candidates in terms of continuing to support them while they are in the race, there's no particular reason to think that Newt Gingrich, say, could deliver his delegates to another candidate. Nor are there any other organized groups within the party who have that sort of relationship with delegates.
"Brokered" conventions evoke thoughts of the pre-reformed process, when delegate chairs absolutely could deliver their entire delegation; that's because most delegates were selected by and represented state or local formal party organizations. Those formal party organizations in turn might have standing arrangements with party-aligned organized interest groups. The idea was that in general what was important wasn't the individual delegates, but the organized groups which controlled blocks of delegates. Really controlled: in most cases, the delegates were bound by prior arrangement to do whatever the delegation boss wanted. At any rate, again in most cases, bucking the boss would have real consequences within the formal party organization.
That simply isn't the case any more. At best, I suspect that Ron Paul's delegates are probably sufficiently dedicated to him that they would do whatever he asks, but even then I'm not sure...and more to the point, each one would be free to choose whatever he or she wanted to do. No one who is in Tampa for the GOP convention this summer is going to lose their job if they defy the state delegation chair, or in most cases suffer any consequences at all for candidate choice in the (extremely unlikely) even that the convention is thrown open. Other, that is, from whatever consequences come from failing to support the winner, especially if that candidate reaches the White House.
Because of all that, if there ever is a convention in which no candidate enters with 50% plus one of the delegates, the outcome would be not only unpredictable, but presumably quite chaotic. Now, it's possible that some set of party leaders (who? who would accept them as leaders?) could sit down and work out a deal in which they all support a compromise candidate, and it's possible that delegates might choose to accept that conclusion. If so, it would be an individual decision by each delegate. It's also possible that full chaos could break out, with no established procedure for pushing delegates to a consensus, and no one with the authority to force delegates to accept a newly-drafted procedure. Really bad results for the party -- a deadlock lasting weeks, the convention splitting in two with each nominating a different candidate and then fighting over ballot slots, all sorts of ugliness -- would all be very possible. We're also talking about 4000 obscure people (more, in the Democrats' case) who would suddenly be reality TV stars. You want to bet that none of them turn out to be deeply embarrassing to the party?
Anyway, back to the main point. If you really have to speculate about this stuff, and I certainly understand the temptation to do so: it's a deadlocked convention, not a brokered convention. There are no brokers. You can't have a brokered convention without brokers. Deadlocked convention. That's the term you want to use.