There are an unlimited number of tackles allowed in Rugby Union and six in Rugby League before the ball is turned over.
Anyone. However, a player who is affiliated to a union side or vise verse cannot play in the opposite code unless they leave that affiliation
Blades are allowed so long as they are plastic, not metal, and do not exceed 21mm in length.
No they prefer fix rubber or aluminum as the nylon stud frequently breaks down and can cause lacerations or embed in players
If you are referring to the "high tackle" which used to be called a stiff arm tackle - then no. If you are caught using this practice its a 10 minute sin bin or if its the second yellow offence -...