Both are defensive backs. The difference is where they line up and what happens when they get it wrong.
Side by Side
| Cornerback | Safety | |
|---|---|---|
| Lines up | Near the line, across from a receiver | Deeper, often 10 to 15 yards back |
| Primary job | Cover one man | Cover space and help others |
| Build | Smaller and faster | Bigger, more physical |
| Run support | Secondary concern | Central to the job, especially strong safety |
| Failure looks like | A receiver running past him | A blown assignment behind everyone |
The Cornerback
Covers a receiver, usually alone, often with no help. It is the most isolated job on defense: when a corner loses, everyone sees it, and it usually costs a long gain.
The skills are speed, hip fluidity to turn and run, and the discipline not to bite on a double move. Elite corners are valuable specifically because they let a defense leave one side of the field alone and commit help elsewhere.
The Safety
Two flavours. The free safety plays center field, reads the quarterback, and is the last line of defense on anything deep. The strong safety plays closer to the line, supports the run, and covers tight ends.
Many teams now use interchangeable safeties who rotate depending on the call, which disguises coverage before the snap.
The Overlap
The line between them has blurred. Hybrid defenders who can cover a slot receiver, tackle in the box and drop deep are among the most valued players in football, because they let a defense change its structure without substituting.
Plenty of college corners move to safety in the NFL when they lack recovery speed but read the game well.
Related
All football positions · The nickel defense · Coverages explained
The Bottom Line
Corners cover men on an island. Safeties cover space and clean up. Corners are built for speed, safeties for physicality, and the best modern defenders do both.