The strap is the trickiest part of this carving. You need to get your head around how the strap 'works', how it's twisted as the cap lies on the table. Then get the main form; then hollow through.
So, as always, take it easy and step by step...
My book, ‘Woodcarving Course & Reference Manual’ (Fox Chapel Publishing 2016 ASIN: B01M6BQFYU) has a similar baseball cap with a buckle at the back rather than a velcro fastening. I strongly recommend it as an alternative look at the project anyway.