Today, this term is generally used to describe a dangerous and therefore stupid form of "fun" practiced by kids trying to emulate the Professional Wrestlers they see on T.V. But, Professional wrestlers are (1) Highly skilled martial artists (2) Professional stuntment (3) Actors. What they do is a performance, not an actual contest. Everything is planned to assure maximum safety for the participants. Of course, as in all sports and stunt work, sometimes professional wrestlers are REALLY injured, but, most of the time, when they appear to be injured, they are not injured at all.
When I was a kid, in the 60's and 70's, "backyard wrestling" referred to the arts of Throw Wrestling
and Submission Wrestling
(not to be confused with Throw Fighting
and Submission Fighting
). These are real sports that require training and rules. Throw Wrestling is similar to Aikido, and Submission Wrestling is similar to JuJitsu. A practicioner of these arts will also be able to defend themself if attacked.