Type of Redshirts "Normal" Redshirt- Can be taken any time for any reason. Most are done freshman year, but there are many cases of them being taken later on. Wrestlers cannot participate in duals or on the "team roster" at an individual event during this time. Injury Redshirt- This will be given if the wrestler has not used the normal redshirt and the wrestler only participated in X% of events. I believe it is something like 25%, but don't hold me to it. You cannot take an injury redshirt and a normal redshirt*. Olympic Redshirt- The NCAA has cracked down on bogus Olympic redshirts by setting criteria for this. The criteria is basically qualifying for the Olympic Trials or being a past World Medalist. Here is the link to the criteria for 2016 http://content.themat.com/forms/2016-Olympic-Redshirt-Criteria.pdf
*6th Year- Normally wrestlers have 5 years to complete 4 years of eligibility. Wrestlers can get a 6th year if they take a normal or injury redshirt, then get an Olympic redshirt. They can also get a 6th year based on injury if they can prove they missed a significant portion of the season due to injury in two separate years. Lastly, they can get a hardship waiver and redshirt such as Jason Tsirtsis did. That one seems very hard to get and I can't remember it being used ever until Tsirtsis' situation.