so i'm sure someone has already thought of this. never the less i'll post it here.
for each turn, a player may either a) place a peice or b) stack as many adjacent stones onto it's nieghbor.
a stacked group is captured if two groups of greater size is stacked next to it.
the game ends when a group reaches a size equal to the number of empty intersections/2, or all enemy stacks have been removed.
the game "starts" only after each player has played at least once. (no passing)

example
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + +
+ + + + + + +
+ + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +

can become
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + +
+ + + + + + +
+ + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +

as another example:
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + +
+ + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +

can become:
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +

but cannot become:
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +
+ + + + + + + + +

Does size mean number of stones or stack height, or sum of heights of connected stacks?

_________________
When you think your opponent has made a mistake, that's when you should be the most cautious.

i think number of stones in a single stack makes the most sense in this context.