Will I defeat a boar?

[Mateusz_Zboj]

My UAC is ~90. My MM is ~50. I have ~400AC and a bronze sword of 87ql.
I also have ~50 STR.

I don't have Tricks and Ruses or Fire and Ice skills.

[Potjeh]

Should be doable if you got enough practice on foxes. Just keep your eye on the advantage scales, boars can tilt it to their side fairly quickly so you need to counter it with Slide or Invocation of Skuld. If you use DoG to get some IP (just make sure you also use Oak Stance and Bloodlust enough to keep your meters filled), it shouldn't take too long to get full advantage and then it's just flexing and punching.

Try your first boar near a boat or other escape route, though.

[TeckXKnight]

You can do it, yes. You're going to panic since it's your first time and that's okay -- just make sure you have some way to escape if you do panic. Wait for it to swing at you and then run to your boat or into your house or behind walls or into a cave or somewhere. It's okay to mess up, just know what your next move is afterwards and learn from your experience.
I don't know your AGI so I'm just going to assume the Boar will have max speed and you'll have minimum.

Enter combat with Death or Glory as your Maneuver and Slide! as your Move. The boar will open with a swing and your defense is going to be Nearly broken by the combination of the boar's attack and the subsequent death or glory. You're going to get pushed down to really low Defense so switch to Oak Stance and once you have ~50% Defense again, switch to Charge!. Keep this up until you have 6 Initiative. Switch to Oak Stance and Flex until your bars are full, then let the boar make another swing and a miss at you. Switch to BloodLust and Flex then throw a Punch. Throw another one once you're at full attack bar again. No matter if you've broken his defense or not, switch back to Oak Stance Flex to buffer against the boar's next attack. After it misses again, repeat your flurry of punches and you should not only break through this time but force it to flee. Chase it down, punching along the way, to claim your victory.

The reasoning is to keep it as simple as possible, to avoid error, while keeping your Defense up. Your attack bar is a valuable commodity to spend in combat until you're ready to attack so don't waste it with an opening punch that it will just immediately recover from. Never let it break your defense bar. For a more experienced combatant it's possible to not only recover but take victory. For someone just getting used to it, it's going to throw you into a huge panic and get you killed. No matter what never just give up. Running away is an option if you need to!

[Mateusz_Zboj]

Hmm, yes you are right the first times are the most exciting.

Also a little anecdote on sudden rush of panic.
After my 30 days holiday I came back to play on my character and wanted to kill a fox.
I trapped it inside a sing trap, but forgot that they can break it when agrroed.
It almost got it if not for the random house in my way. That's why I think I should ask/think first before rushing into battle...

Also do you think bringing tea mugs with ql 33 tea would be good idea?

[TeckXKnight]

Also do you think bringing tea mugs with ql 33 tea would be good idea?

It certainly won't hurt but it shouldn't help either. You're not going to be running out of stamina.
I should add that this is far from the ideal method of hunting boar. It is neither the fastest nor the safest method, it is just the simplest at your skill level. It only requires some very basic maneuver and move swaps without going into special moves. Best of luck!