Clicking 'R' on the keyboard to input a radius when using the Circle Tool closes ArcMap.
This is a known issue. Clicking 'R' before clicking on the screen causes ArcMap to close.
- Click the Circle Tool from the Advanced Editing Toolbar.
- Click on the screen to locate the center of the new circle.
- Click the 'R' key to open the Radius dialog.
- Enter a radius value and click Enter.