Surface Elo
also: clay Elo · grass Elo · hard court Elo
The same Elo, counted only from matches on one surface: a clay rating, a grass rating and a hard-court rating per player.
Some players are much stronger on one surface than another, and an overall rating averages that away. A surface rating replays only the matches on that surface, with its own K schedule counted from the matches on it, so a clay specialist's clay rating sits well above their overall one.
Both numbers are stored before and after every match, and get_ratings ranks the tours by either. Grass has the fewest matches a year, so grass ratings move the most and are the least settled.
A surface rating built on a dozen matches is mostly its starting value. Check the surface match count (returned with every surface rating) before reading much into it.
Where to get it
Related
Surface Elo from the API
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