I've recently taken up goju-ryu karate. In sparring, I'm often matched up with someone significantly taller than myself (by a foot or more), and find that I have trouble finding openings due to their relatively easy access to striking (oftentimes hammer strike) at my head when I close the distance.
It may simply be due to my having less experience, but are there any strategies I can use to close the distance without making it easy for my taller opponents to strike my head?
Much of sparring is a cat-and-mouse game. If something is working for them, try to get them to rely on it and do it when it's not quite an ideal distance/time/angle. Just knowing they're likely to try it means you don't need to be as spontaneously creative and can plan and practice some counter measures.
Some things to try:
feint closing (and maybe pull back your front hand a little as if you'll slide into a jab or whatever), wait for their technique while out of range, then close
feint closing, if they look to use a hand technique then kick under their arms from the edge of their reach: front leg front and side kicks are good options
feint closing, if they use a linear punch or hook, grasp their attacking arm and pull them/you together as you deliver a front leg kick
when you do close, make it explosive and initially towards them, but arc increasingly sideways as you get close (this way you close fast and it's less obvious that you'll be moving sideways when they notice you start to move, so it's harder for them to stay facing you or line up a counter at the right angle)
think about how they're striking and choosing footwork and blocks that make it easy to deal with the strike and will leave you in a good position: e.g. if the strike is a right downward hammerfist with a very vertical descent, you would ideally deflect from your left to right (closing their striking arm across their body) with your right forearm while sliding your body to your left (so you get "blind side" advantage at or behind their right shoulder); if it's a jab a simple palm block while sliding forwards past it should work well too - basically, try to integrate a deflection with the distance-closing footwork
work on timing: back away so they're having to chase you a little - make them not only over-reach with their attacks, but plonk their feet forwards with larger, cruder steps: try to time an attack or close as their weight's settling onto a foot they're moving forwards - it may be momentarily hard for them to use the back leg/arm (if they've been drawn a little more side-on during the step), and they can't kick with that front leg unless they have very good balance and haven't stepped too far past their back leg; that means you should have free use of all four of your limbs to deal with mainly their jab (but always keep your front shin ready to jam any front-leg kick they might deliver as you close); consider e.g. gliding side kick into their ribs as you close
use low kicks to unbalance and distract them as or before you close (they may well do it back to you, then it's up to you to use distancing, checks, footwork etc to outclass them)
Their knees. Taller opponent's are forced to protect their lower extremities from smaller opponents who make themselves smaller to attack further below themselves especially when smaller opponents begin to circle around them to attack them behind. Be careful this type of attack can put you in more dangerous fight.