The above answer is not technically wrong, but it's probably not the right way to think about solving the problem. The general idea of a multicam clip is that you want to switch from one view to another view to another view. Each camera is a valid view and interchangeable with one another AS A VIEW. Cutting back and forth between a player and the clock is a great example of switching views.
The general idea of a compositing digital video editor is that you can build a final image from layers of video, text, graphics, etc. And you can even use such things for controlling effects like keys, transitions, etc. Very cool!
If the idea is to have one clip function as a picture-in-picture view of a clock, then the idea of using a multicam clip as the source for that clock is kinda wonky: why have a multicam clip whose job is merely to select precisely a single view?
If your footage of the event is continuous (and even multi-camera), then that would make for a good baseline track, such as Video Track 1 (V1). Place the footage of the clock on V2, aligning it so that it is synchronized with the video in V1. Initially, V2 will completely cover the video of V1, giving you a very exciting view of just the clock for the whole duration of the game. Using the Inspector in the edit window, scale the clock to the size of the picture-in-picture view you want (using the Zoom controls), but don't adjust its location with Position X and Position Y. Rather, adjust its location with Anchor X and Anchor Y.
When you have the clock where you want it to becreate a compound clip consisting of the clock clip and the action clip (which might be a multicam clip if you have a multicamera recording crew). Now you can edit the compound clip, cutting out all the boring parts. You might decide that you don't want the clock on all the time, only at certain times. You can edit the compound clip, making cuts to define the regions where you don't want the clock to show. Or making cuts where you want only the clock to show--full size. If you want a full-sized clock, make cuts so you can select the part of the clock clip you want to be full-sized. Set the zoom factor to 1.0 and the clock will magically fill the screen in the center (because you used the Anchor XY instead of Position XY controls).