My take, the crowd looked very bored, very catatonic before Trump arrived. Then when he arrived, they transitioned to just listless.
The first 1/3 of his speech was boring and standard Trump stuff. at the 2/3 mark he started getting interesting with by deviating. For the final third the speech was superb.
I only caught the last 15 or 20 minutes and it looks to me like he had the crowd eating out of his hand... the event was billed as a pep rally and it certainly seemed like he got them motivated.
yes it wasn’t a speech for the ages, it was just him speaking off the cuff... and as far as I can tell he excited the crowd, which is what a pep rally is for.
Sorry, I watched the same speech and saw no boredom or listlessness. Maybe you were watching a Jeb townhall.