Odd one.. accounts differ depending on who you ask and on which side of the fence you sit, but this is how I saw it.
Player/Manager had previously been sin binned for something they believed to be fairly innocuous, not too sure of the exact offence.
Early in the second half there was a further disagreement between the ref and Player/Manager whilst he was inactive on the sideline, he was cautioned for his troubles. After laughing at the ref and some further chit chat the yellow was upgraded to a red.
Offending player refused to leave despite numerous requests and from what I could hear was using some fairly antagonising language towards the ref (not swearing I might add, but it looked confrontational). From there game was abandoned.