punch above (one's) weight
1. To perform, achieve, or do something at a level that is considered beyond one's abilities, talents, or personal attributes. The small-town mayor has been punching above her weight recently, going head-to-head with federal lawmakers over the issue of immigration reform.
2. To be romantically or sexually involved with someone who is considered by others to be superior in physical appearance, intelligence, or success. I think Janet's new boyfriend is a model or something. She's really punching above her weight!