Is "to practice volleyball requires stamina" grammatical?

Is the sentence "to practice volleyball requires stamina" grammatically correct? As opposed to the sentence "practicing volleyball requires stamina"?

Another example:

• To ensure safety requires strict observance of rules.
• Ensuring safety requires strict observance of rules.

It's grammatically correct to use an infinitive as the subject of a sentence, but that example sounds awkward. It's tough to come up with a rule. Parallels between infinitives sound fine ("To understand all is to forgive all"), and there are other cases. If you rephrase your example with an antecedent pronoun ("It requires stamina to practice volleyball"), it sounds more normal.

A Complement clause of any type (infinitive, gerund, tensed that-clause, or tensed wh-clause) can be used either as subject, object, or object of preposition (i.e, they are noun clauses). But they only occur with certain verbs -- everything about complement clauses is governed by the matrix verb they are the subject or the object of.

The OP question is one variety out of many ways a clause might come to be a subject. It's common to want to use predicates that indicate properties like is fun, takes a lot of time, or requires stamina to talk about athletic activities.

Such activities are mostly verbs, so they need a verb phrase, and every verb phrase determines a clause. This is what infinitives and gerunds are for. But which to use?

As McCawley 1998 puts it (p.126)

Roughly speaking,
• that-complements correspond to propositions
• for-to complements [infinitives] correspond to situation types
• 's-ing complements [gerunds] correspond to events

So gerunds are more common than infinitives as subjects denoting events like practicing volleyball, and

• Practicing volleyball requires stamina.

with a gerund instead of an infinitive subject, is therefore a much more common and totally unexceptional way to say the same thing. In general, gerund subjects are more common than infinitive subjects.

However, that's not to say that infinitive subjects are ungrammatical or incorrect -- they're just shaped wrong. An infinitive subject has to begin with to, because otherwise the listener won't know it's the subject:

• To have done so much so young is phenomenal.
• *Have done so much so young is phenomenal.

Anyway, English finds that configuration distasteful. English would much rather have a short subject, thank you very much, and it wants that first verb in the verb chain to be the second constituent, if you please. The place for long complicated clauses is the end of the sentence; English is right-branching.

So there are a whole bunch of syntactic rules that move heavy constituents to the end, often leaving a dummy behind. In the case of the OP question, that rule is Extraposition, which moves an infinitive subject to the end of the sentence, leaving behind a dummy It subject.

• To practice volleyball requires stamina.
    =(Extraposition)=>
  It requires stamina to practice volleyball.