Don't forget that HMF basic will always call another assist. I have seen from 0 to maybe 15 assists off outrider's first move.
Maybe not completely explained by Ragnarok_COTF above, the profundity 20% chance of assist can happen off any yellow (crit) number you see pop up from an attack. Not just one per attack. So when Outrider does its concussion missiles it is possible for that one attack to result in 5 assists.
If falcon assists Outrider, and then falcon calls Outrider, that's Outrider using an ability on its own turn again, so falcon again has 50% chance to assist. Outrider probably did another 3 crits...
It can really roll on, and that 15 assist I've seen may have only stopped because the enemy ship was gone.