Thoughts on Combat Momentum

 I was reading about the Encounters Die and it occurred to me that no games really capture momentum. If you read a story about sports (or even combat) the side doing well is said to have the momentum. This is mostly confidence for those that have momentum combined with lack of confidence for those that do not have momentum. That is where the momentum die comes in. 

The Momentum die is an old-style d20 numbered 1-10 twice. One color is dedicated to each side in the combat. If the die is one sides color they add the value to their To Hit rolls (fighters can take it as a addition to damage instead if they want), and the other side subtracts the value. 

1. When combat starts the d20 is at 0 (placed where everyone can see it). 
2. During the first round of combat the GM compares the successful hits for each side. Subtracts one from the other and moves the Momentum dice total that many numbers in that direction. For example the characters hit 4, their enemies 1, so the die moves 3 points in the characters direction. The Momentum die goes from 0 to 3 in the Characters color (characters now get +3 To Hit, enemies are -3 To Hit. The next round the characters hit twice, the enemies hit 3 times. 1 point in the enemy direction turns that 3 to a 2 (characters now have +2, enemies -2). The characters still have momentum but not as great. This repeats every round until the numbers are high enough one side always wins momentum which should move the die to 10 before long.
3. If one side gets a 10 momentum the other side rolls morale.

That's it. This makes being outnumbered particularly hairy, it might shorten combat or make it extra long, I can't be sure until its tested. I'm willing to take suggestions if anyone has any ideas that might improve it.