Defending Against Spellcasters, Part II

2. Getting next to the spellcaster and readying an attack in case he starts casting makes combat casting useless (since you're not using an attack of opportunity). This is also a great tactic to use if you have a ranged weapon handy because the spellcaster won't simply be able to take a 5-foot step to get away from you. However, if you lose line-of-sight, you're still out of luck.