The phrase "giving leg up" is often associated with providing assistance or support to someone in need. However, antonyms for this phrase might include hindering, obstructing, or impeding. Rather than facilitating someone's progress, these opposing actions could create obstacles and setbacks. Other antonyms could be failing to support or neglecting to help when someone is struggling. It is important to recognize the impact of our actions, whether helpful or harmful, and to strive towards being a positive influence in the lives of those around us.