Matt Leinert did only take 1 class in what was his 5th year. The NCAA only required 12 credits/semester for athletes during their 1st 4 years. In their 5th year, they only need to be registered with the school and take at least 1 class (at least in football). I'd have to assume baseball has the same requirements??
My son is a freshman redshirt (medical) pitcher this year and he's talking about either taking grad classes or taking additonal undergrad classes to get a double major during his 5th year. The school is giving him pretty good money, along with academic $$, so i have no problem shelling out the difference for his 5th year. As someone said, they'll be working the rest of their life, they might as well enjoy college for 1 more year.