The phrase "put one foot down" can be replaced with its antonyms depending on the context. If we are talking about someone who is indecisive or wavering, we can use antonyms such as hesitate, vacillate, or waver. On the other hand, if we are referring to someone who is resolute or determined, we can use antonyms such as stand firm, hold ground, or stand one's ground. Similarly, if we are talking about someone who is yielding or acquiescent, antonyms such as surrender, give up or give in can be used. The choice of antonyms depends on the context of the situation and the emotions conveyed by the speaker or writer.