math question and the effect on over/under percentages..please help

[DrSues02]

I'm working with an NHL database to come up with some over/under percentages for various periods. I have all of the games from this current season for every time broken down by period.

I then have these calculated to determine that teams Over or Under 1.5 percentage, a line that is commonly offered for each period.

Then, I have a summary page where I can average the values for two teams who will be playing that day:

Example: Detroit goes under 54.55% of the time and PHI goes under 43.64% of the time.
If they are playing each other, that becomes an average of 49.09% on the under.

I hope everyone can follow me so far. Everything seem logical up to this point?

Then, since many NHL teams use various goalies, I have an average of each teams goals allowed per game. Det might give up 2.61 goals per game...this number is an average of ALL the goaltenders they might use during the season.

I want to use the goaltender for THAT particular game. If Goalie #1 gives up 3.09 goals per game, he would be 118.39% ABOVE the average for the team.

Therefore, the team would theoretically give up more shots and the game would go OVER more often than average.

Everyone following this?

My problem: How do I incorporate this goalie number into the averages I have for the OVER/Under?

I've tried taking the average of the two goalies (say its 105% above their teams averages), then multiplying that by the current over/under percentage.

An example:

Goalies:
DET MACDONALD 118.39%
PHI LEIGHTON 100.18%
Average for the combined goalies:
109.28%

O/U:
49.09% 50.91%

Weighted by Goalies:
O/U:
53.65% 55.64%

Basically, multiplying 109.28% by the O/U numbers adds 9.28% to the total. However, as u can see, the %'s no longer add up to 100%.

Anyone have any ideas or thoughts on where I'm going with this?

Please let me know. I've spent a very long time working on this.

Thanks.

DrSues02