Wow...an accident...a shitty one, but an accident nonetheless...
How sparring and "special sparring" usually works at my gym is usually a two/three-fold:
1) lack of communication...people are just unaware of how hard they should be going. Without proper instruction, people think sparring is "just going at it"...so they try and KO each other...this is usually a beginner mistake.
Corrective action: Talk with your partner more...if you're more experienced, make sure they know full-well that sparring is a safe, yet realistic way to practice technique with each other...not an attempt to knock their damn head off
2) Escalation...people agree, "Ok, we're just gonna go 75%" and someone tags the other a bit too hard...then from there, they go a bit harder, etc. etc...
Corrective action: Don't be a dick and apologize if you're the one that tagged the other too hard...don't be a pu$$y and be a dick if you're the one that got tagged too hard...make sure both partners are ok, communicate that it was an accident and apology accepted, and continue as was...
3) Trainer puts more experienced guy with "new guy who thinks he's a badass"...the "new guy who thinks he's a badass" usually just goes entirely too hard with another newb he's paired up with and thinks he's the $#!t b/c he's "beating someone up" (even though it's just simple drilling)...our trainer will usually then put that ego-maniac with someone far more experienced and tell them "Make sure he keeps his hands up" or "Teach him how to defend low-kicks"...this isn't really an issue, it's just a matter of putting someone in their place...
Corrective action: None...just do what your coach tells you and make sure he keeps his hands up...chances are, the "new guy going too hard" will be the one who's all about escalation AND they don't understand the purpose of sparring...help him along the way...but be "firm" with your attacks...
I think, above all, training partners should just communicate more. If you're far more experienced than someone, let them know and ask them how hard they'd want to spar...if you're new, be humble, introduce yourself to your partner and make sure you're on the same page when it comes to drilling and sparring...
I don't get it sometimes, it's as if people forget simple concepts about how to conduct themselves just b/c they're in a place where you practice combat...