Can an average student crack CAT?

Yes, average students can crack CAT. Students who get through CAT at one go, have the right aptitude for CAT, which was built over time. They have been practicing Maths right from their school days and have been avid readers. 

If you are average at your studies, you need to spend a lot of time practicing, in order to score good percentile in CAT. Most students usually have gaps in Maths or DILR or English. You need to put in the extra hours to bridge the gap. Find out the subjects in which you are weak, clear the basics, and practice as much as you can. 

It depends on what you mean by average. If you want to get a call from IIM ABC, you will need to score at least 99.5% in CAT. So, you will have to score above 99.5% of the test takers. With proper preparation and the right strategy, you can definitely do it.