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
1 more definition
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