How to calculate the win probability of a sports team when playing at home/away?

Hi,

I need Excel to calculate the win probability of a sports team when playing at home/away, but this is not as simple as I hoped. I have various columns in my excel spreadsheet (which is attached), one of them being Home/Away (so under this column, you would have H if the team in context was playing that specific game at home, and A if the team was paying that specific game away), another one being Win/Loss (W in a cell underneath this column header would signify a win, and L would signify a loss). How would I use these columns in an excel function to work out the win probability when playing at home ie the total number of wins at home, divided by, the total number of games at home.

I have attached the spreadsheet for you guys to take a look at

Thanks