They were drowned out.
A UFC bout might have looked like a safe space for Trump. Here’s why it wasn’t:
The booing began immediately. The music on the loudspeakers was turned up, either to herald Trump’s arrival or to stifle the crowd’s displeasure in reaction to it, but the sound of those boos was overwhelming. A few Trump fans scattered throughout the room cheered, but they were drowned out. Three rows down, a young couple held up a sign that said “Impeach and Remove.” There was no introduction like there had been at the World Series last week, no sense of ceremony or occasion, no video of the president and his sons on the Jumbotron, no “Lock him up” chants — but for a moment, the environment, already full of alcohol and flush with three hours of fights and charged for more, felt volatile.
This is why Trump continues to hold rallies – they’re the only places where people aren’t booing him.