Yes, you can wear leggings on United (but airline can police your clothing).

United Airlines: leggings ban 'not sexist' even though it affects women more, US news

Outrage, Explanations After United Turns Away Girls From Flight For Wearing Leggings : The Two-Way : NPR

United Airlines Says 'Your Leggings Are Welcome' After Teen Girls Barred From Flight For Wearing Them

FRIDAY PONTE POCKET LEGGING

Woman claims she was 'harassed' by American Airlines staff, told to remove 'f**k you' sweatpants

United Airlines caught up in leggings row - BBC News

FRIDAY PONTE POCKET LEGGING

Leggings Take a Victory Lap - The New York Times

Why The Outrage Over United Shouldn't Have Legs

Leggings on United Airlines: See Which Stars Wear Leggings to Fly

Hey, United Airlines! Your Leggings “Dress Code” Is Not Only Offensive, But Also Not on Trend

Teens Wearing Leggings Not Allowed To Board United Airlines Flight

Do you wear tights or leggings under your dress? - Quora

Why United Airlines can get away with treating its customers like garbage - Vox