The phrase "weak side" refers to the side of something that is considered less strong or less powerful than the other side. It suggests a lack of strength or effectiveness compared to the opposite side. Full definition
The main purpose for making comparison is to extract some strong and weak sides of comparable objects and to make conclusions concerning some particular features. (essaywriter.org)
They're fighting relegation, but there are at least three weaker sides in the division so far. (latestchelseanews.com)
Playing against weak side bottom 10 sides, this sort of team would score a lot of games. (justarsenal.com)