Conspiracy theories abound!
As it turns out, the Trumps had Cruz's speech beforehand, and knew it wasn't going to endorse Donald. They then instructed the New York delegation to erupt into boos at a certain place in Cruz's speech
If you love our country, and love our children as much as you do, stand, and speak, and vote your conscience, vote for candidates up and down the ticket who you trust to defend our freedom, and to be faithful to the constitution.
Booing erupts, but ONLY from the New York delegates.
Cruz, visibly surprised:
I appreciate the enthusiasm of the New York delegation.
Note: theoretically, nobody except the Convention coordinators (the Trump campaign) knows what's in the speech- for all the New Yorkers know, the next sentence could be a ringing endorsement of Trump.
Chants break out against Cruz's wife, who has to be escorted out: "Goldman Sachs! Goldman Sachs!" Kind of a bizarre thing to 'spontaneously' come to mind.
Trump makes an entrance, the music swells, spotlights turn to him, the lights onstage fade, leaving Cruz standing there in the dimness.
Trump immediately starts tweeting, including about Cruz being almost assaulted and being turned away by Sheldon Adelson.
Would Donald be the kind of guy that would organise this to try to humiliate Cruz that way? You betcha.
The only thing is that he apparently didn't realise that the spin would be: Republicans split; Ted Cruz honourable martyr to his conscience.