To buy a NFL jerseys the same way you would buy yourself a t-shirt. NFL Jerseys should fit much differently. Having a jersey that is too big is better than having one that is too small. When wearing a football jersey, it should be loose fitting, hanging from the shoulders. Of course, don't buy a size that is much too big for you either. Oh, and never tuck the jersey into your pants.
The Difference Between Authentic vs. Replica: Hockey jerseys, like most other sports jerseys, are available to the public in two forms. The thentic" versions are much more expensive than the "replica" versions. Basically, authentic jerseys come with sewn on numbers and logos, whereas replicas are printed. A good-quality replica is absolutely fine to buy, but if you have the extra money to spend, an authentic jersey lasts longer.