Only problem is RAW that U cannot ever affect unwilling targets. . .which means if the U is affecting my fist (attack is target), rather than the person I'm aiming to punch (defender is target), by RAW it would fail every time the attacker decided they were unwilling (which, unless it were a play fight, would be every time)
I concur that an RR is not appropriate, nor indicated by the spell. . .which indicates to me that the flaw lies in targeting the attack, rather than targeting the person to be defended.
The rules on passive/informational spells won't allow you to affect someone's mind (like mind domination, forget, etc, without an RR) it will allow you to pick up information without changing or otherwise affecting anything.
Generally you cast them in a prior phase, or use the interrupted/changed action rules to stop some other action to cast one.
often:
Fighter declares 70/30 OB/DB and will move up on snap, attack the Mage on deliberate.
Mage could declare casting the bladeturn on snap, or some other actions. . .then cancel the other action to cast the bladeturn in snap or normal. . .though IMO if the latter, they need to beat the fighter's initiative to get the bladeturn in normal off before the attack in normal.