Grenades
In addition to you main weapons, you also have these toys to play with. They vary greatly in function and explosive power. What class you play affects what grenades you get - the heavier the class the more explosive power you carry. However, the grenades you get are tailored closely to what class you are playing - if you don't have severe explosive power then the grenades you have will have functionality very suitable for your class. So, learn them well and your effectiveness will get better and better.

NB - Damage radius is measured in floor tiles times 2. For example, look at the blue tiles in 2fort in your base. If a grenade has a damage radius of 11 then if you're closer than 5.5 tiles away, you'll be affected by the grenade. It seems to be a conveniant and universal way of measuring distance.

A quick word here about spam - heavy, powerful grenades allow you to do a LOT of damage to enemies - yes, you can just go in, chuck a few about, get a few kills then die. And do it again. And again. A word of advice. Please don't. You may be racking up plenty of kills but it's plain annoying and pointless. You are not helping your team, you are just being a pain and you may as well go and play deathmatch. Go for the flag, go for the key and use grenades to defend yourself and take out sentries, hang around in defence and use them to take out attackers but don't just use them to rack up kills and nothing else. I don't mean to preach but it makes a big difference.