If I remember it right, in Elric it is impossible to parry with a flail.
I think it should be like this in RQ too. In real use, flails were used
with a shield. So they were not used for parrying. After all, the handle
is way too small and it does not have a "cross" like a sword. the
chain-ball -end of the weapon is too heavy for fast moves.
So in my mind a character using a flail has to use a shield also. On
the other hand, 2-h flails have long handles which can be parried with.