Yoga and static stretching, or passive stretching as I refer to it, is not "bad" per se, but must simply be used correctly and at the right time for the most effective results. You may find the following former post of mine a helpful introduction of the relationship between passive and dynamic flexibility.
"Passive stretching is definitely a component of my flexibility program, just not the major emphasis. My athletes begin a program comprised on passive flexibility, active flexibility, basic strength, static strength and dynamic strength from the first day that they walk into the gym (In fact this physical development, takes precedence over any and all skill development). It is easier of course to build flexibility in younger athletes, however that flexibility must be balanced with strength to allow that athlete to successfully mature into a National level (or higher) competitor.
Care must be taken to not weaken the joints through excessive passive stretching. Focusing on active flexibility ensures that the joint's level of strength increases right along with its flexibility. For athletic purposes, I would rather have a "strong" beginning athlete with tight joints than one who is naturally "loose". With correct training, I can develop the required flexiblity in the "tight" athlete.
As a side note, I have found that passive flexibility training only, past a certain point, has little effect on a very strong athlete or the very tight (a category that most adults would fall into), while active flexibility and dynamic stretching movements result in much greater and faster results without compromising their strength levels (or in other words, weakening the amount of leverage they can bring to bear on an athletic movement).
For adults, I have found that they as well respond much better to a mixture of passive and active flexibility. An example would be stretching a "pike". Training the stiff leg deadlift with a pause at the bottom or windmills done with legs nearly straight usually gives much faster flexibility results than simply sitting in a pike on the floor and stretching. The same with wall walks for bridge flexibility as opposed to simply pushing up into a bridge.
In my opinion, the body performs best from a foundation of strength and this seems to apply to flexibility training as well."
Yours in Fitness,