How to beat Chaos Space Marines using Tau?

Chaos Space Marines are deadly in close combat, and most likely (Me being a Chaos player) will try to get Berserkers across the field ASAP, if we get into close combat, your going to have to play smart by using crysis suits with Close range hit and run attacks. Kroot are worthless againsts Berserkers or just pretty much any CC Chaos Unit. Tau's killing power is at range, if you roll 1's again and again. Odds are, your men are going to die for the Greater Good. If the Chaos player is using possessed, you need not be to worried about it. They're a plague on any Chaos player's army list.

From the Tau perspective (me being an IG and Tau Player) there are two things to keep in mind against Chaos. The first is that they'll be coming to you. The second is that your Crisis Suits (Plasma and Missile, or Plasma and Fusion) are the big killers against them, and the killing range for your Crisis Suits with Plasma rifles is when they hit rapid fire at 12". The real trick is not to fear close combat - manage it. Use Railguns to kill as many tansports as possible, then expendible blocking units like Piranhas, Kroot and Drones to slow down squads of Berserkers and screen your valuable units, then wipe them out in manageable chunks with the Crisis Suits. Think of it like this: by trying to enter close combat, your opponent is putting himself into the range band (12"-18") where you are best able to kill him. You want to back up, yes - but not too far! Hold him in that band as long as possible, pouring on the rapid fire, without letting him actually assault your crisis suits. So long as you can ensure (through manuever, screening and blocking) no more than one or two enemy units make it into range of you every turn, you should be able to handle them.

Basically you have to stay mobile and funnel the enemy in, so you can defeat him one manageable chunk at a time.