When you build that basement wall with economy lumber, and one stud is just not flat with the others, there is a way to fix that quickly to end up with a flat wall.
IDENTIFY THE BULGING OUT SIDE OF ANY STUD
Then in the middle of the bow, saw cut about 2/3rds of the way through the stud. Drive a glued wedge into the saw cut by pulling back on the stud as you insert the wedge. You are lengthening the board on the inside of the curve, and not changing it on the outside, which causes it to bend -- straight. If you go too far, just back out the wedge. Once the wall is flat, screw boards onto either side of the cut area to make the fix permanent and strong.
SORT YOUR LUMBER BEFORE STARTING