I thought it was well explained, when I wrote "you can select 2 players to represent your club in this challenge" at the end of the seasonw e will sum up the assistances that both players earned, and this will decide who wins the challenge.
There was till middle season to select the 2 candidates, then, ofc. there's a luck factor, but too, the way we manage the team can help a particular player in that sense, seelcting them for corner positions, FKs, or focussing the passing etc
This is how it works SuperDunk,