Punt/kick Returners

I know we don’t pick who is our return man and Sandbox picks that player for us. I never had return man last season so I used Street Free Agent. Since I do have a few options this season for my returner, do I have just one returner for every game for the season, or will Sandbox pick a new returner, of those on the roster, every single game?

If a player returns just a couple of kicks/punts for the season, will he be an option that Sandbox will pick for my returner? Is there some minimum of returns that is needed before Sandbox will use him as the returner for each of my games?

The computer picks the best punt returner on your team with respect to average yards per return. There is a minimum number to qualify, but I decide the minimum threshold each year while processing the data. Players must qualify separately for kickoff returns and punt returns.

Thank you!