Residual Plots. What's going on.

I'm running some analysis on grades in different subjects and seeing if being involved in this outside activity has an impact on grades. I am looking at residuals for a regression I ran and getting this skewed residual plot. Any ideas what's going on? View attachment 5666


Ambassador to the humans
It's not "skewed". It shows lines which indicate that your response is discrete. Is there a specific issue you're worried about?