To form or become covered by a scab, as of a wound. That scrape is scabbing over so it can heal, but it can't do that if you keep picking at it! You need to apply pressure to stop the blood from flowing so fast, or else the cut will never be able to scab over.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
[for a wound] to form a scab. The wound soon scabbed over and the injury was well on its way to healing. I hope this shaving cut scabs over before I have to leave for work.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
To become covered by a scab: The wound scabbed over and eventually healed.
The American Heritage® Dictionary of Phrasal Verbs. Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.