[RPG] counterspell a Subtle spell without material components

Put him in armor he's not proficient in.

In 5e you cannot cast spells while wearing armor you're not proficient in. So unless the sorcerer has dipped Fighter and is therefore proficient in all armor (one of the quirks of 5e), wearing armor he's not proficient in renders him unable to cast spells. Plus, the armor makes it more difficult for him to escape without the time to remove it. Make sure to keep him tied up at all times though. So when adventuring it pays to bring along some extra armor, just in case you encounter evil enemy spellcasters (or evil Druids in earlier editions, where Druids became unable to cast spells or Wild Shape when wearing metal armor).

Note that this will work only once, and a savvy DM will have his villains minor in Fighter while attening Evil Spellcaster School to get a workaround for this.

The rule on spellcasting does not say that you need a component, but:

Each spell's description indicates whether it requires verbal(V), somatic(S), or material(M) components. (PHB 203)

So technically there could be a spell that does not list any components. Subtle spell overwrites even the above rule, which it can do as a class ability is more specific than a base rule (specific beats general, PHB 7).

Another way to put this: in the description of subtle spell "without any somatic or verbal components" should be read as "without providing any somatic or verbal components". It is clearly meant as a way circumvent the normal rules of casting. What you propose would limit casting on the other hand, which clashes with this being a class ability.