After looking at the video I would have to think it’s possibly a PCL tear. I had a similar injury in hockey as well and mine was a Grade 3 PCL and grade 2 LCL tear. When the shin is pushed back like that in a collision, the PCL is the one that bears the brunt of the impact.
I can’t see it being an ACL tear as usually that is associated with a twisting type impact or movement. If there is a ligament to have damage, the PCL is one that is easier to come back from and at times surgery isn’t even done. For surgery on a PCL tear isn’t always successful.
X-ray would just show negative on a break. MRI will show the ligament info.
Oh and I am still not confident in Smith as the playoff starter.