OP Score on OP.GG is basically a performance rating for a League of Legends match, usually on a 0 to 10 scale. It estimates how well you played using in- game stats and different aspects of your match, not just kills or deaths alone.

What it measures

OP.GG says the score is based on summoner stats and overall in-game performance, with factors that can include kills, deaths, assists, CS, gold earned, damage, wards, objective damage, role, and laning phase.

How it is used

At the end of a match, the highest-scoring player on the winning team gets MVP , and the highest-scoring player on the losing team gets ACE.

Timeline OP Score

OP.GG also has a timeline version that tracks performance over time during the match, updating every 5 minutes on Summoner’s Rift and every 3 minutes in ARAM. The final score at the end of the game becomes the official OP Score.

Important caveat

OP.GG notes the system is still in beta, so it can sometimes be inaccurate depending on the game.

TL;DR: OP Score measures your overall in-game impact in a match, using a mix of combat stats, farming, economy, vision, and objective-related performance rather than one single stat.