It's called "round_ranks" and uses the format:
idx = userid of player in position x
scx = score of player in position x
Only supports 16 players since I didn't realize servers could have more when I made it, but should suit your needs just fine.
// Tell plugins the userIDs of who finished in what place on the round report.
"round_ranks"
{
"isfinal" "bool" // If true, this was the match report and thus the culmination of all the rounds played this map.
"id1" "short" // Player ID of whoever finished in first place
"sc1" "short" // Score of whoever finished in first place
"id2" "short"
"sc2" "short"
"id3" "short"
"sc3" "short"
"id4" "short"
"sc4" "short"
"id5" "short"
"sc5" "short"
"id6" "short"
"sc6" "short"
"id7" "short"
"sc7" "short"
"id8" "short"
"sc8" "short"
"id9" "short"
"sc9" "short"
"id10" "short"
"sc10" "short"
"id11" "short"
"sc11" "short"
"id12" "short"
"sc12" "short"
"id13" "short"
"sc13" "short"
"id14" "short"
"sc14" "short"
"id15" "short"
"sc15" "short"
"id16" "short"
"sc16" "short"
}
All of our custom events are located in "gesource/resource/modevents.res", so if you're wondering if we have a specific event to hook that's not included in the core source engine, that's the place to look. Good luck with whatever you're making, it sounds interesting!