You have to realize that Spider-Man has really none advantages in here.
In terms of fighting smarts, Namor is above him.
Spider-Man's strength is miniscule compared to Namor.
I haven't seen an proof that Spider-Man is faster, then Namor who can hit you dozen times in a moment and move his limbs fast enough to propel himself through water with Mach speeds.
Even if Spider-Man would be REEEEEALLLY angry, his punches would not cause Namor anything else then just an mild pain.
Can Spider-Man even escape Namor? Namor flies with speeds that outclass WWII fighters.
I don't think Spider-Man has a shot here.