Is it wrong to clap after someone is baptized?
Clapping is a way of showing approval or appreciation. We generally use clapping to show approval to something that entertained us, but it can be used for other things we approve. As such it isn't particularly wrong, but I do have a concern when people only use clapping and don't make any effort to tell the person directly that they are happy to have them as part of the family of God.
"I say to you that likewise there will be more joy in heaven over one sinner who repents than over ninety-nine just persons who need no repentance" (Luke 15:7).