A sports team that is significantly better than most other teams in their respective league, but fall short of being the best.
In a direct matchup against the best team, they are the underdog.
In college football, LSU and Georgia are the overdogs of the Southeastern Conference. They are better than most other teams in the conference, yet are mostly overshadowed by Alabama.
A door wall is a sliding-glass door or patio door. The term is yet another example of banal Michigan vernacular, where in the residents latch on to company names, trademark names, marketing terms and product names from local companies. The terms become embedded in the local vocabulary and eventually become accepted as actual valid words and phrases. In this case the term comes from Wallside Windows in Taylor, MI (a large window manufacturer), where 'door wall' is their created word for sliding-glass door.
"Bob! John's gonna bring over them doorwalls from Wallsides on Tuesdee afternoon 'round two-thirty. Get 'er done!"