neck guard

noun3

1. •
   A piece of armor or protective equipment which protects the neck.

   • […] and even though she did eventually agree, she had one rule: I had to wear a neck guard or a neck roll [to play football]. — 2019
2. •
   A part of a helmet (of mail, plate, etc) which extends down to protect the neck.
3. •
   A ridge or an additional plate on a shoulder piece which projects upward to protect the neck: see passguard.

   • The pauldrons, or shoulder defences, show the slight upright neck guards, erroneously called pasguards. The rerebras and vambras protecting the upper and fore arms have faint spiral ridges on them […] — 1898