From the video

Video: Everything You Need to Know Before Week 3 Fantasy Football (Rookie Report)
I thought maybe it was an ACL tear... it's a hamstring strain... Tom Pelisero is really positive here, saying the team isn't even ruling him out for next Monday's game against the Eagles.
Mentioned at 15:08 – 16:21Captured by STACKED 5 hr after posting

STACKED’s take

Negative signalInjury

Hamstring strain; likely out Monday vs. Eagles; replacement offers more predictable offense.

Williams suffered a hamstring strain in Week 2 (initially feared to be ACL or Achilles tear). Tom Pelisero reported the team isn't ruling him out for Monday's game vs. Eagles, though the source's baseline expectation is he'll miss that game and possibly one or two more. Avoiding IR would be a huge win given how the injury looked. Additionally, Williams is known for high time to throw and scrambling ability, which creates unpredictable offensive outcomes; his replacement Tyson Bagent will likely provide more steady, first-read-focused production that Ben Johnson can control more directly.

Caleb Williams headshotCaleb WilliamsQB · CHIPlayer page — value, ADP, projections, and every insight