Tennis stats lie if you don't filter by surface. The same player can have a 75% hold rate on hard courts and 55% on clay — that's not inconsistency, that's physics.

What changes on clay

Lower hold % for everyone — the slower bounce neutralizes serves
Higher break % — return time advantage is huge
Longer rallies — average rally length doubles vs hard court
More winners required — you cannot end points with placement alone

What changes on hard court

Higher hold % — flatter, faster bounce favors the server
Lower break % — second serves can still be big weapons
Shorter rallies — first-strike tennis dominates
Tiebreaks more common — sets get closer when both players hold easily

How to use the surface filter

In Tennis Log's Stats tab, switch the surface filter and compare your hold/break numbers. A healthy gap is 5-15 percentage points between hard and clay. Bigger than that and you have a surface-specific weakness worth addressing.

Tactical takeaways

On clay, your fitness and patience matter more than your serve
On hard court, your first serve and return position matter most
On grass (rare for amateurs), serve and volley actually still works

Filter your stats by surface every time you analyze them. It's the single highest-value filter in the app.