[The Wrathchild]

IIRC it is also thought to include those blows that do not connect solidly, even if they are on target. edit - actually, no - see Kromm further below.

Also, remember that this is the chance while retaining the ability to defend. It's easy enough to hit if you All-Out (Determined), or in the case of using the Martial Arts, using Telegraphic Strikes.

The interpretation would often be that what unskilled brawlers are really doing IRL is trade All-Out Attacks, with 90% chance of hitting, roughly. Using the MA rules this might be seen as Telegraphic Committed Attacks.

Retaining defence is more complicated as much more body stuff needs to be coordinated.