Apple Final Cut Pro X (10.0.9) - Manual (Page 125)

Chapter 8 Edit your project 125
Cut multiple selected clips at once
You can use the Blade command to cut selected primary storyline clips and connected
clips simultaneously.
1 In the Timeline, select the clips you want to cut.
2 Move the skimmer to the frame where you want to cut.
3 Choose Edit > Blade (or press Command-B).
The selected clips are cut at the skimmer position.
Note: If you don’t make a selection, this command acts only on the clip in the primary storyline.