But it’s hard to draw the line nowadays. What about the well worn line ‘but the 3 Peaks fell race is a trail race’? Snowdon and Ingleborough fell races definitely are too.
Its only in the U.K. that you really have a distinction anyway - trail races in the US and Europe include some very very big mountains. Theoretically it’s only because our mountains are comparatively tame that we are more able to leave trails and go open fell. I suspect going off trail high in the Rocky Mountains might be a tad more tricky (as well as a bit more rattle snakey, beary and cougary)