"Se piglio" is not a complete sentence.
Anyway, 'pigliare' , is an old/popular form for
'prendere' (to take) or 'acchiappare' (to catch)
'If I take...' or 'If I catch ...'
A familiar expression is (rather old fashioned)
'Se ti piglio ...'
'If I catch you...'
said for example to a naughty child as he is running away