(It was) Because it was the first day

Mrs. Baker: Justin, don't feel bad about today.
Mr. Baker: What happened?
Mrs. Baker: He joined the basketball club, and it was his first day, and they didn't let him go near the court.
Justin: All I did was collect balls from the floor, and watch the others play.
Mrs. Baker: Because it was the first day. Most first years don't play much in the beginning.
Justin: Yeah, I see.
Mrs. Baker: It's like that everywhere. (to her husband) Honey, back me up here.

I'd like to know "it was" is implied before "Because."
Thank you in advance for your help.