The phrase "to overturn the deficit" means to change a situation where you owe more or have less than what you need or want, and turn it around to have more or to be in a positive position. Full definition
So their chances of overturning their deficit in this high profile tie isn't great. (football-bookmakers.com)
Having suffered a humiliating 5 - 1 defeat in the first leg of the Champions League Round of 16 encounter against Bayern Munich, Arsenal virtually stand no chance of overturning the deficit in the return leg at the Emirates Stadium on Tuesday night. (arsenallatest.com)
It is true that our forwards have not been scoring enough goals which makes me worried about our ability to overturn our deficit against Monaco. (justarsenal.com)