My take on this.....
Starc started giving it mouth the ball before, sledge time!
Pollard probablly pulled out (early enough for Starc to see) next ball to pay him back for Starc being a mouthy muppet previous ball!
Starc had a rush of blood and gave Pollard a scare by following him and bowling him. Was he aiming for him or aiming to just get close to him with the ball? Only Starc knows for sure! But he shouldn't have bowled it, particularly as Pollard has his back turned, and therefore had little protection from a 90mph ball!

Pollard was rightly livid and went to throw the bat, but pulled out at the last second, as sanity just about won through in time!
Starc high-tailed it quickly back to his mark as he'd realised that he had gone way too far!
Pollard was still livid as he could have ended up injured through Starc's stupidity.
Who was in the wrong? BOTH of them!
Starc was obviously in the wrong for the reasons outlined.
Pollard was also in the wrong as he reacted very poorly when he almost threw the bat - that is also unforgivable!
I know that people see throwing a bat as more dangerous than what Starc did.....but I would rather be 20 meters away from somneone throwing a bat at me than having someone bowl a 90mph ball at me with my back turned! The bat wouldn't be travelling that fast and could avoid that. Whereas a 90mph ball hitting you on your back or another unprotected bit of your body would be agonising at best, and the injury could be nasty!
I see Starc as the main culprit in this one! But both need to be kicked in line quickly and bring them down to Earth!