As Joseph Kell says, it needs to be an aspect on the target itself. The reason most people use manoeuvres is that it gives them a free tag, allowing them to grapple someone without a fate point.
Rather than use a manoeuvre, you can cause a consequence and then tag
that to grapple someone. So just hit them rather than 'knocking them off balance' and rely on strength to deal enough damage. The benefit of this is that dealing that extra damage can shorten the fight considerably, it's just a little unreliable as you must deal enough stress to cause a consequence. This works better with a strength power.
Alternatively, you can make an assessment to find a weak point, either by finding an existing aspect (like the aforementioned 'athletically challenged') or by declaring that you've seen a weak spot (using your fists skill to declare that they have a 'weak guard', or alertness to spot that they have 'untied laces'). The benefit of this is that you can make the assessment in the social conflict before the fight, or you can even make the declaration on the main bad guy three sessions before the final fight and, as long as it's a relevant one (as they'll probably tie their shoes eventually) it'll still be there for the fight.
Finally, you could create a stunt that allows you to call someone out as a supplemental action, just like wrestlers do before a match. The 'psych out' would place a fragile manoeuvre that could be tagged for the grapple, but you'd get a -1 on the roll for it being supplemental unless he has a speed power. You could do this as a standard manoeuvre using intimidation but it'll take an exchange again.
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Oh and Joseph Kell also says, just give him a belt of strength or something. It'll massively increase his grappling power! Inhuman strength is only -2 and will give him a higher chance of causing consequences as well as dealing much more damage in the grapple, while increasing his chances of holding the grapple itself. Basically for any successful grappler you pretty much
have to have strength!
Make it an enchanted wrestling belt, say he won it in a wrestling match with a fae, or even with an old demi-god thing. That sort of thing happens all the time in greek myths
. As a wrestler he learns of a wrestling competition while having a drink in a bar, not realising he was in the accorded neutral ground and that he was surrounded by supernatural types of all sorts. They egg on him, thinking it would be funny, but he manages to win and it so impressed the judges that they reward him with the belt. Unfortunately he is tripping over the supernatural all the time now, as winning the belt seems to have made him the fae's favourite toy.
F.W.F Wrestling belt. (Fae Wrestling Federation).
One time discount is +1 if it's a normal looking belt to wear; +2 if it's a large, gold wrestling trophy belt.
So:
[+1] One time discount
[-2] Inhuman Strength
or:
[+2] One time discount
[-4] Supernatural Strength