*You may not be able to get this while connected to Live due to a bug in Valve's servers. If that is the case, unplug your Ethernet connection/wireless adapter or stay signed out of Live and try again*
When playing as a hunter, you can deal damage from the actual pounce you make onto a survivor. You can inflict up to 25 points of instant damage onto a survivor from making a good pounce. The damage you do while on top of a survivor and "punching" them does not count for this achievement, it has to be 25 points of pounce-damage.
Using two controllers, or, if you can get it to pop online, substitute Guest account with a friend on Live...
In Crash Course, play on Split screen versus with your main account (the one you want the achievement on) playing as infected.
With your Guest account playing as a survivor, kill all of the other survivors (this way when you miss as the hunter, they won't kill you and you get another go at it.) Now park yourself up against the guard rail between the end of the guard rail and where the helicopter is laying. (See video for placement.) Leave this account there until you get the achievement.
With your main account, get killed until you become the Hunter and climb up the building at the beginning of Crash Course as shown in the video. It is the two story warehouse that is next to the crashed helicopter. When you are on the roof, stand a few feet back from the ledge and crouch. Aim up into the sky right around the moon and then pounce. As you jump you need to quickly aim down and until your target reticule is on the survivor. Once you land on the survivor it should indicate you've inflicted 25 pounce damage and the achievement should pop up.
When I did this, the only problem I had was missing my target. All you have to do is adjust how you are aiming once you are in the air. Once you get that down, you should be able to get the achievement no problem the first time you successfully pounce that survivor.
It took me about 5 tries to get the jump right.