The above video has been around since 2009, although the original source is unknown. It claims to show a golf ball hitting a steel plate at 150 mph. It almost looks like a water balloon. However if we compare it to other videos of golf balls hitting things at the same or faster speeds, we can see this it is not what it is claimed.
Here's a real ball being hit at 175 mph (video at 1:19)
And another more similar to the first, of a ball hitting steel at 150mph.
This fact has been pointed out many times over the years. Each time the video comes up (either the first upload in 2009, or later copies) someone will point out that it's not real. But still it gets repeated and shared
What the video most likely is is a foam practice ball.
These balls look just like regular golf balls but are lighter and more flexible, so are safe for indoor use, or practice outside in limited space.
Is it possible though that this is a video of an actual golf ball, just one travelling faster, like 300mph? Intuitively not, as you'd expect the golf ball to crack or explode if it hits something so much faster than designed, and the amount of distortion does not look possible for the semi-rigid shell of a real ball.
But can we prove it? Well one physical number we know about gold balls is the "coefficient of restitution" (CoR) which at it's simplest the fraction of the speed the ball will have after it bounces off a large hard heavy object like a steel wall. In practice the equations are more complex using vector arithmetic, and the CoR really applies to two objects, and you have to take their mass into account. But the CoR of a golf ball hitting a golf club is usually given as around 0.83 (the legal limit placed by the USGA)
Here things are complicated slightly by the relatively light steel plate moving after being hit, however we can analyze the various motions before and after the bounce by picking appropriate frames with the least frame-to-frame deformation of the ball.
Here the two dots indicate the position of the ball (and the plate) at six frames apart (where a frame is something that actually moves in the youtube video, not the 30 fps video itself). We can see the ball bounces back from the plate with a relative velocity (i.e the speed relative to the now moving plate) of much less than the original velocity. In fact it's about a quarter. We can't do the exact math without knowing the mass of the object, however it's quite safe to conclude that this is not a regulation golf ball.
[UPDATE 2019] I'm not entirely sure the above is correct. This video shows large amounts of deformation, although not as much as is shown above.