In MLG settings there are fragmentation and sticky grenades. Sticky grenades have the ability to stay attached to an opponent if they hit them - a guaranteed kill. There’s no secret to the sticky grenade. All you can do to improve your "stick rate" is to get in and find a feel for the grenade's trajectory and try to stick people whenever you have a chance. If you’re fortunate enough to stick an opponent near his or her teammate, an easy double kill will result.