Support player is a role. Xyp is a great example of this role, or maybe NBK. Support player is a player who most of the times plays anchor on CT side, like B on Train, B on Vertigo, ramp on Nuke, B apps on Mirage, the guy who is holding the bombiste where no one goes, and when they go there they rush him and he gets 1 kills and gets traded.
On T side he is the one who flashes for the team, when you go for B rush, support player is the one who will flash and go last, so he can clutch, or throws himself first for his team, but wont go second or third, thats where the star player is going.
Support is there just to fill the gap. Trust me, I am playing this role for my entire life. I hate entrying, but I am reallly good at clutching, so I always go last, so then I can have 1v2 clutch situation. On CT I am playing B apps, I have no action there, and I am often times the one who is in 1v1 or 1v2 retake on A or I am saving.
Support is a role.