On op
From Scriptwiki
The on OP event triggers when a user on a channel is opped.
on <level>:OP:<#[,#]>:<commands>
$opnick refers to the user who was oped.
Example
Triggers when a user with level 999 was opped in #help.script or #mIRC and deops him again:
on 999:OP:#help.script,#mIRC: { mode $chan -o $opnick }
See Also
On deop triggers when a user was deopped.