Detect drones passing through hula-hops
Detecting the drone by having it break a light beam sounds like the way to go.  It should be easy enough to build emitters and detectors into the hoop.  If the drones are small relative to the size of the hoop, then you need multiple light beams so that any drone within the hoop will break at least one of them.

Three emitters might be enough with sufficient detectors spaced around.  You blip each emitter for a short time, then look for the signal from the detectors immediately before each blip, during, and after.  There needs to be enough of a rise during the blip relative to before and after to consider the particular beam unbroken.

Each blip shouldn't need to be more than a microsecond or maybe a few, depending on the settling time and therefore noise immunity you want from the detectors.  Let's say doing a complete blip with before, after, and during measurements takes 20 &micro;s.  Actually I think it could easily be half that, but I'm tyring to start with pessimistic values to see where this is at.  With 3 emitters, that means you can check all light beams every 60 &micro;s, or 17 kHz rate.  That should be good enough.

To do a sanity check on that, let's see how fast a drone would have to be going to move 10 mm during one scan cycle.  (10 mm)/(60 &micro;s) = 167 m/s.  That sounds quite fast for a drone, and they should occlude a beam over more than just 10 mm.  Note that at the speed of sound, a drone would only move about 20 mm during one scan cycle.