Is this a new installation of Steam with CrossOver Games 8, or did you have an existing Steam bottle created with an earlier version of CrossOver Games? If you've used earlier versions, did TF2 work with them?
Also, what kind of Mac do you have and what kind of graphics card does it have?
A brute force technique you can try is to create a new bottle and install Steam and TF2 into that, from scratch. That might fix any junk or corruption that may have somehow gotten into the registry of your existing bottle.
For a less drastic approach, you can run regedit and delete the key [HKEY_CURRENT_USER\Software\Valve\Source\tf]. That will reset TF2's settings, which may be bad.
If that still doesn't work, we can investigate further.