Smurfing has always been a problem and is especially prevalent in this game being f2p. Games like csgo you can use a phone number to verify your account and be only matched against other verified accounts. I remember in the past when it was brought up people mentioned not wanting to give a number to riot to be a reason but with premier league needing a number that doesn't seem like too strong of an argument.

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Of course phone verified accounts will not eliminate smurfing but I think it will be a descent enough hoop such that there is a reduction of incidents.