My definition of the free market is the absence of coercion (ie all actors are free), not whether people should be allowed or not to sign contracts you think may distort it which seems pretty subjective. I think making people not free to sign no-poaching contracts they willingly want to would be the distortion here, the no-poaching agreements may or may not have a negative effect overall but that is not a distortion of the free market. The only characteristic of the free market is that it is free, not that it is inefficient or not. The theory is that free markets tend to be more efficient, but they are not always so.