These excessive rules that stifle creativity.
to suppress or prevent something from happening (Sometimes the *ing form is used without clarification to describe an environment that makes it difficult for people to express themselves freely.)
or more specifically:
to smother or prevent someone from breathing (Sometimes the *ing form is used without clarification to describe an environment that is so hot or humid that it makes it hard to breath.)
Much more rarely, to stifle is used in the context of anatomy to refer to a four-legged animal’s equivalent of the human knee (the joint between the upper and lower leg).