Whats the deal with facial expressions

I watched the highlights of Lakers/Nuggets game 3.  With a minute to go, and the Lakers down by two, Kobe Bryant has the ball at the 3-point line, dribbles about three times, and then makes a three pointer.  

It was dramatic.  It was a game winner.  And then he did something totally surprising.  He made a facial expression that I'm still trying to understand the meaning of.  He glared and jutted his lower jaw out while huffing air pretty hard.  And I just can't figure out the mindset that would make that expression.  

Its a fun game to try to mimic someones facial expressions; it really gives you an idea of the emotions they are feeling.  It is a useful tool for figuring out how people really feel about a situation.  Words say one thing.  The face tells reality.  One can pick up on subtle emotions, signs of defeat, of defiance, etc.  

And Kobes facial expression?  I have no idea what it means.  

The closest thing I can think of is that of a wounded animal, or a person who was just tackled and hit but is now on his feet after fighting off an attacker.  That same glaring, defiant, but also scared? look.