The biggest difference between boots is Soft Ground (SG) and Firm Ground (FG)
SG – Soft Ground Boots:
Designed specifically for play on soft, natural surfaces found during most of the rugby season in the U.S. and UK. Usually, soft ground boots have replaceable aluminum studs.
Designed for play on synthetic 3G and 4G pitches as well as firm, natural surfaces found in sunny, dry southern hemisphere conditions. Typically, firm ground boots have molded, permanent studs made of rubber or another non-metal material.
8 studs in a 6x2 formation make these boots sturdy. Forward boots typically have longer studs, providing greater grip, which is ideal for play in rucks, mauls and scrums.
Back Boots:
6 studs with a 4x2 layout reduces the weight of the boots. The studs are typically shorter, which also makes the boot lighter and allows for faster movement and pivoting.
Legally, multi-sport boots with studs that meet rugby's requirements may be worn on the rugby pitch. However, rugby boots provide more stability and support and are preferable for playing certain positions, especially in the back.
When trying on boots, it is important that they fit tightly and snugly without being uncomfortable. However, if your feet are still growing, as is the case with children and teenagers, it is a good idea to give a little space for growth.