It is probably not “protective” but leash reactivity.
I would always start by training an acceptable replacement behavior (targeting my hand and making eye contact are two. that I like to use – a down-stay or even just a pet trick are fine alternatives) in a completely distraction-free environment.
Then I would go for a walk in a place where there is likely to be a trigger that is predictable. I would ask for the replacement behavior and reward it well at random times on that walk, and then when the “trigger” appeared I would retreat past the magic “no reaction” line and get the behavior and reward. Then I would step just barely into the reaction zone and do it again. If the puppy didn’t do it, I would give a reasonably hard correction, step out of the zone, get the behavior and reward. Then back in, then out, etc, and once I had the behavior while the puppy was “on alert” to the trigger there would be the equivalent of a party and we would go on our merry way.
Lather, rinse, repeat, over many, many, many walks.
The goal is to make the “reaction zone” shrink and the default behavior something that involves a behavior that is calm and/or tuning to you instead of to the trigger.
Also, for a leash reactive dog: DO NOT keep the leash tight. That only increases the feeling of being trapped/stressed. Keep the collar high on the dog’s neck to increase the effectiveness of any collar correction and decrease the risk of tracheal damage if the dog lunges. Keep the leash loose but also short so you are dealing with the start of a lunge instead of a dog with 5–6′ to accelerate before hitting the end of the leash.
Here is good collar placement:
Here is good leash handling: