Petitioners are claiming that they have enough signatures to get a recall against Ferguson Mayor James Knowles III on the ballot, collecting about 2200. They need 1828, which gives them about a 17% cushion (I believe they have more time to boost that total). Signature rejection rates differ, usually from state. In some states, a 10-15% cushion seems to be sufficient. In others, we've seen 40% failures. I have never seen stats for Missouri, so this could be anywhere on the map.
None of the articles that I've seen mention the question of whether a court might toss out a recall if Knowles challenges it. See here for much more details on this angle. There is strong reason to think that the recall may not be upheld by a court.