not rejoin play unless he was temporarily replaced to have bleeding controlled; a player who has been substituted may return temporarily, to replace a player who has a blood injury or has suffered a concussion, or permanently, if he is replacing a front-row forward. In international matches, eight replacements are allowed; in domestic or cross-border tournaments, at the discretion of the responsible national union(s), the number of replacements may be nominated to a maximum of eight, of whom three must be sufficiently trained and experienced to provide cover for the three front row positions. Prior to 2016, all substitutions, no matter the cause, counted against the limit during a match. In 2016, World Rugby changed the law so that substitutions made to replace a player deemed unable to continue due to foul play by the opposition would no longer count against the match limit. This change was introduced in January of that year in the Southern Hemisphere and June in the Northern Hemisphere. Equipment The most basic items of equipment for a game of rugby union are the ball itself, a rugby shirt (also known as a "jersey"), rugby shorts, socks, and boots. The rugby ball is oval in shape (technically a prolate spheroid), and is made up of four panels. The ball was historically made of leather, but in the modern era most games use a ball made from a synthetic material. World Rugby lays out specific dimensions for the ball, in length, in circumference of length and in circumference of width. Rugby boots have soles with studs to allow grip on the turf of the pitch. The studs may be either metal or plastic but must not have any sharp edges or ridges. Protective equipment is optional and strictly regulated. The most common items are mouthguards, which are worn by almost all players, and are compulsory in some rugby-playing nations. Other protective items that are permitted include headgear; thin (not more than 10 mm thick), non-rigid shoulder pads and shin guards; which are worn underneath socks. Bandages or tape can be worn to support or protect injuries; some players wear tape around the head to protect the ears in scrums and rucks. Female players may also wear chest pads. Although not worn for protection, some types of fingerless mitts are allowed to aid grip. It is the responsibility of the match officials to check players' clothing and equipment