Checking the anim state seemed to be an elegant solution, but there was something strange happening when I tried it, which I blame on my lax coding skills.
In case anyone is interested, I ended up using the speed solution, as -
- create trigger, set activation to INDEPENDENT (my player character is GUE named p1)
- CONDITION is
(speed p1) >= 8;
- ON ACT. is
Resistance setFriend [East, 0]; East setFriend [Resistance, 0];
...and viola! Instant Assassin's Creed.
Thanks everyone for your help.