[Bruno]

You definitely should be able to, at least with appropriate equipment. Clinch knives specifically exist to be concealed-carry knives worn in locations that are easily accessed when pinned, with sheathes that not only help with Holdout but also make them possible to draw when you're in that totally awkward position.
Of course, they're also the epitome of the Small Knife, if not even smaller. The point of the clinch knife (har har) is that if you've been tackled, or grabbed from behind, and at least one arm is either free or only partly pinned more-or-less near your waist or armpit (the usual places to wear a clinch knife) you can get it out and poke your opponent enough to make them let go from pain and surprise.