Explosives are the only weapons that have, as you may expect, an explosion effect. Currently, the frag grenade, which is the default and only grenade, is the only available explosive. More explosives such as more types of grenades as well as shoulder launched weapons will be added in the future. As of the moment, all players spawn with 3 grenades available to them, regardless of class chosen. Do not be fooled the glitch that only shows the amount of grenades you had in the previous life after you re-spawn (for example, if you used 2 grenades in one life, when you respawn, the glitch will say that you only have one grenade). You will always have 3 grenades when you spawn no matter what.
Tips and Tricks
The grenade is used by pressing G, and an animation plays with your character pulling out a grenade and removing its pin, and then throwing it. It explodes 5 seconds after being thrown (which is indicated by the "ticking" cross hairs as you cook it in your hand), and does enough damage to instantly kill full health enemies who are too close to it when it detonates.
The in-game grenade doesn't explode upon impact, as it has an internal timer, so you can aim it towards a wall and bounce it off that wall, onto a position that may not be reachable otherwise without moving into the enemy's line of sight.
Cooking A Grenade
However, if you hold down G, then you will "cook" the grenade, shortening the time the grenade takes to explode once out of your hand. If you hold down G too long, the grenade will blow up in your hand resulting in a suicide Frag Kill, which in the majority of cases you probably won't want. The aiming crosshair will move 5 times in a little out-in movement and it will explode on the 5th one. You should throw it where enemies are at because that way, you have cooked a grenade and the enemies will have less time to react to the grenade because by cooking the grenade, the fuse is shortened and therefore the time to explode is shortened. To be a little bit annoying, you can cook a grenade and run into someone. The person will kill you, but since you're holding a grenade, it will drop on to your corpse and if you're lucky, the adversary will have no time to react and the grenade will explode whist killing him. Be careful not to hold down too long when throwing at longer distances because the grenade may explode early.
Where to use Grenades
Use grenades wherever there are too many enemies to take out with guns. The best tactics for throwing grenades are to time it right so that it explodes where your enemies are. That can be tricky when you have a bunch of guys rushing you. You will never be able to throw a grenade when someone is shooting at you- it takes way to long, and you'll find yourself taken out pretty quickly. The best way to throw a grenade is to do it calmly and think of where you will bounce it off of or just lob it at. Sometimes, lob a grenade into busy areas. Who knows? You might just even get a kill!