I think so - especially because it came off white first - knock on by white onto blue's hand - I think it was clearly not in blue's control and it would be a real stretch to say that he had knocked it forward deliberately...
Change the situation a little, and lets say white never touched it and blue did just knock it over his head
- personally I am with OB.. you can't deliberately knock (or indeed throw) the ball over a player's head and regather it the other side.
- others say you can -- but are therefore liable to be tackled while you are juggling.
Caveat - you ask
is he entitled to knock it up and forward intending to regather possession?
my answer is that if this happened in the middle of the field - ie trying to catch a loose pass, then yes, but he can't deliberately knock it forward over the head of an opponent. This is why this is tricky!
Interesting that people are trying to answer this by gut feel, without focusing on what the law does and does not allow. Relevant law is all in Law 12:
[LAWS]DEFINITION: KNOCK-ON
A knock-on occurs when a player loses possession of the ball and it goes
forward, or when a player hits the ball forward with the hand or arm, or when the
ball hits the hand or arm and goes forward, and the ball touches the ground or
another player before the original player can catch it.
DEFINITION: THROW FORWARD
A throw forward occurs when a player throws or passes the ball forward.
‘Forward’ means towards the opposing team’s dead ball line. [/LAWS]
We see that the law very clearly intends to address two separate and distinct matters, which are carefully defined to allow us to differentiate between them.
[LAWS]12.1(f) Intentional knock or throw forward. A player must not intentionally knock the ball forward with hand or arm, nor throw forward.
Sanction: Penalty kick. A penalty try must be awarded if the offence prevents a try that would probably otherwise have been scored[/LAWS]
The difficulty we face here is that it is neither a knock-on nor a throw forward as defined. It is a hybrid - the knock-forward. Was that deliberate - to introduce a 3rd, undefined element? It is the precursor to the knock-on, and it makes sense. All WR need to do is to include it in the definitions, and 12.1(f) is as clear as a bell. For me, as for many others, the law nonetheless makes sense without the additional definition; it works better for the game as a whole than if the defined tern Knock-On was used, leaving the knock-forward unclear; and it is consistent with the intent of the game. Juggling becomes an unintentionally effort, and any deliberate juggle is shown as illegal, regardless of whether the effort turns into a Knock-On.