Probability of outcome of Sporting event

Hello,

I have a question or problem to resolve and I am not an expert in math so if this isn't the right forum to post this, apologies.

Problem:

How can we evaluate the probabilities of the result of a sporting event based on the current score.

For example.

Lets say the probabilities of team A vs. team B winning the event at the start were the following, team A 70% and team B 30% (No draw or tie possible).

The first team to score 21 points would win the match (no tie-breaks or win by 2 clear points rules)...

How could we calculate the relative probabilities of the outcome during the game as the points change...

For example, after 10 minutes of exciting play....

Team A 5-1 Team B...

what would be the probabilities of Team A winning considering it started the game with 70% probabilities and is now winning 5-1? etc...

The 3 variables would be.

- Starting probabilities

- total points needed to win

- Current score

Thanks

Alex