With regards to your allegation that the officer HAD to have entered on a red light, how do you know? It's possible that he began his turn on a yellow, or had to yield for other traffic. You admit, yourself, that you had looked away and were not paying attention until you suddenly looked up and started your turn on a green. Therefore, you'd be guessing as to what the officer may or may not have done.
You are free to contest the cite, and even to play the games that AgentSmithers suggests. However, keep in mind that if you do go to trial and lose, you will likely lose the opportunity for traffic school.
However, that being said, I can't understand how the officer might argue a violation of VC 21453(a) if you did not cross the limit line until after the light was green. Had you pulled out in front of the officer, that should have been another code section. If the officer testifies to an unsafe turn, then you should prevail on VC 21453(a).
There's either something more to this, or, the officer was a dunderhead, or, you had stopped over the limit line in the first place.
I'm sorry I'm really bad at explaining things thoroughly.
These are the reasons why I know that the police officer ran a red light:
1. I take the same route home everyday. The light for my side of the road doesn't turn green unless the left turn lane the officer was making a left on turns RED.
2. I understand my dad can't be used as a witness, but he was right behind me and saw the whole thing.
3. From the moment I looked down and the moment I looked back up was literally 1 second or 2 at most...
The police officer just couldn't have been where he had been with out running a red light. It's literally common sense. It my not be common sense when you don't have all the facts, and I would like to apologize if I wasn't clear enough.