Does flexibility increase speed

Answer 1

Correct type of stretching will definitely help develop speed. Reciprocal Inhibition of the Antagonist muscle with its Agonist.

Ideal Tension Length relationship between Agonist

and Antagonist will produce the best contraction, this is not to say a Olympic Weight lifter needs to be supple or flexible he or she only needs to have the correct length /Tension between Agonist

and Antagonist of Primary movers for specific sport. Stretching at the wrong time or the incorrect muscle for a given sport will hinder performance. Have you ever noticed for example a 100 meter sprinter will stretch their Hamstrings at the starting blocks but never their quadriceps? This is because it would prevent optimal contraction of this very powerful group of leg muscles.
It is best to seek a expert to prevent incorrect stretching protocol.