When a drunk person is persistently looking at you out of the corner of their eye.
"Boy I could feel John sideballing me all night while I was talking to Bill, he's got to get over it!"
di BRC 06 ottobre 2005
To look out the corner of your eyes at someone so that they "can't tell your looking"
I changed my radiator in the parking lot of the apartment complex. Noone said anything, but alot of people were sideballing.
di Tug33 18 maggio 2011