By being in the class A team is stating that she is a person addicted to a class A drug; Heroin or cocaine. As ed sheeran has stated "I wanted to write it so it sounded kind of upbeat, so you wouldn't really know what it's about, because it's quite a dark subject."A drug like crack cocaine is called a 'class A' drug. That's in the same category as heroin. Instead of making it clear and just saying what the problem was, I'd say, 'She's in the 'class A' team.' It was kind of my way of covering up (a person's addiction), I guess, making it a bit more subtle."