Basically what has already been mentioned. There's ranked tiers in League: Bronze, Silver, Gold, Platinum, Diamond, Masters, and Challenger. Each of those has 5 subdivisions within them numbered 1-5 except Masters and Challenger. As it stands currently, unless you're ranked at least Diamond 1 (and even then...) you basically won't get scouted for an esports at all, professionally speaking. Ideally you'll have to reach Masters minimum if you want any existing esports team for League to feel like they should even consider glancing at you, let alone offer you a tryout or anything.
Beyond that, there's other avenues of playing esports than just strictly trying to get into Challenger tier and hoping you're noticed by a team coach/manager/player passing by. While it is certainly not NA LCS (North American League Championship Series) there is a collegiate outlet for League here in NA so it is possible to not be Masters or Challenger and play on a college team instead if your university happens to have one or there is a growing interest in starting one. The official League of Legends website has links to give you info on which schools have teams/esports clubs and then from there it's up to said school what their requirements may or may not be for you to be on the team.
The 3rd option is always money. Regardless of your "rank" you won't be denied a team and a chance to participate if you can afford to do so. Doesn't mean you won't get outright stomped, but hey if you got money and some friends by all means attempt to win a legit tournament and try to make a name for yourself that way.