In general we may propose three scenarios to classify cases when players have higher success on the second serve serve than on the first serve;
- "Borg-Pecci scenario" - second serves are so few that returner cannot get into a groove,
-"chance" scenario - second serves are so few that the serves higher success rate behind the second serve may be obtained purely by chance,
- "mystery" scenario
- there were many second serves in a match and we have no idea why servers' succes behind these serves was so high.
I am afraid that usually the third scenario is valid.