how to hard reboot MacBook PRO
How to hard reboot a MacBook Pro
iPad, iOS 5.1.1
What do you mean by hard reboot?
What are you trying to accomplish?
Usually, holding down the power button for 5 secs while your MacBook Pro is running will shut it down - only if it freezes. Otherwise shutting it down and turning it back on is a hard reboot.
See link below.
http://osxdaily.com/2014/10/06/force-reboot-frozen-mac/
Now if you're talking about doing a NVRAM reset - that's a totally different procedure altogether.