The word "out-stripping" means surpassing or outpacing someone or something in a certain activity or race. Its antonyms, on the other hand, refer to actions that are slower or less successful in comparison. Some antonyms for out-stripping include lagging, falling behind, trailing, slowing down, and losing ground. These words convey the opposite meaning of out-stripping and suggest a lack of progress or achievement. So, if you're looking to describe a situation where someone or something is not excelling or leading, you may consider using one of these antonyms instead of out-stripping.