A lot of the early primaries are proportional, but with a 15% cutoff for getting delegates; here's my June post on the issue. The odd prospect is that if only one candidate gets 15%, he (or she) gets all the delegates.
Right now, that's where The Donald is nationally, the only guy over 15%. The night is still young, but that's a sobering thought.
What might be even odder is the prospect of no one getting delegates and the whole delegation being uncommitted; that would be the case if Trump comes back down to earth and no one getting 15%. Eventually, some of the lesser candidates will drop out, but with ten candidates getting 4% or higher and second being 11%, all of those folks are a good debate or two from being the lead alternative, so such a even split could continue for a bit.
In that case, as I said when I looked at it in June-
If the winner only clocked in at 13%, it would seem that all the delegates would be unpledged and the delegate-selection process would be political trench warfare with each faction looking get their folks heading to the convention.
That's looking like a real possibility. Given modern hygiene, we'd be looking at smoke-free smoke-filled rooms in a lot of places.