When evaluating player performance on clay surfaces, the most important metrics include win-loss records on clay, service games won, break points converted, and percentage of points won on both first and second serves. Other key indicators are the player's movement efficiency, expressed through stats like unforced errors and winners, as well as the ability to construct points and engage in longer rallies, which are more prevalent on clay. Additionally, examining the player's overall physical fitness, injury history, and adaptability to the slower playing conditions and heightened spin characteristic of clay courts can provide insights into their effectiveness on this surface.