In Rashi D"H Meshalshin B'mamon (at the top of the amud) he provides 2 explanations. My chavrusa and I could not understand the first pshat at all. It seems like all the Rishonim explain like the 2nd one.

Does anyone understand this first pshat in Rashi?

Any help would be appreciated.

edaf on that amud

I would seem Rashi’s 1st Pshat is as follows. That Bais Din becomes a "third party" for the witnesses which are now have to deal how to split the payment. SO BD being the 3rd party splits the payments evenly among the litigants (witnesses.)