In this video I think it's demonstrated incredibly powerfully what importance needs to be placed upon anti-horse tools.
The horses do the bulk of the work in creating space that allows the police line to tighten the noose here. Without them they never would have controlled these crowds with people on multiple sides of them. They could not have maintained control.
There must be simply and effective methods to spook these horses without causing a danger to them. Something that could be deployed that would make the riders tell their superiors "we can't deploy because the horses would be spooked by x".
Anyway. What are other people's thoughts here? Obviously this protest was unprepared for a fight (although several police have been hospitalised). What could small groups of 1-5 have done in the wider engagement to make things go differently?
I think tripping them would depend on how heavy the line is and how well secured it is, as well as what the horse is doing. The kinetic energy of a horse at gallop is... impressive.
I think someone who has more personal experience with horses would be better able to answer if it would spook them.
Edit: I suppose more of a net arrangement with cans on the end could be effective, as the horse's legs would be entangled and the noise would follow them, which should spook them.
Although I mentioned in another answer below, horses in a blind panic are incredibly dangerous. If one panics into a crowd at full speed, people will die, between the horse & the ensuing crowd stampede and possible crush. Human stampedes are deadly! The Hillsborough disaster killed 96 people, for example.