The Lights as a screening force had always faced a tough one-sided job and were meant to taunt rather than tangle full-on with the Legion:
After a round of fighting they retreated/retired, either forcibly by combat outcome or under PIP orders, to end up laying behind the main Greek battle line inadvertently protecting the baggage (which as "fast" was allowed to follow behind the Greek box formation) and rear of the army (somewhat nullifying the threat posed by the Samnite sweeping arc).
In the middle the armies set to with a great shove of pike:
The Elephants roaring:
With the Knights causing pressure:
And the Legion starts to take casualties:
But just when the hour is darkest for the Romans, there is a glimmer of light as disaster befalls the Greek left flank, the "would be" Alexander goes down to the Roman cavalry generals sword on a straight 6 to 1. Sub-command demoralisation and carnage follows:
The Greek Knights are now diverted from their Legion bashing to fight for their lives. Simultaneously over on the other flank (off camera) a portion of the mighty Phalanx is destroyed as Roman Spear and Auxillia flank it. It all hangs in the balance.
Next: End Game