I think the OP should have meant the Xander character itself, not the actor playing him. The Xander character was the most uncomfortable in the 1st season and gradually got more comfortable. In the same vein, I think the OP is correct that the Xander character was more uncomfortable in the first season and grew out of that in the second season. Xander grew into his role in the Scooby gang as soon as "When She Was Bad" (Season 2 2000season premiere) versus "Prophecy Girl" (season finale of Season 1) and not just because of his haircut. One only has to see his declaration of love to Buffy in "Prophecy Girl" and you can see how uncomfortable Xander was. But in high school everyone evolves. I was a geek as a freshman with no friends but then I played football the next season and was popular with many friends. I was a different person as a freshman than I was as a sophomore. In Season 1, Xander was a sophomore in high school and then he became a junior in Season 2. This should not be an indictment on Nicholas Brendon who played the role better than anyone could: I honestly believe Ryan Reynolds would not have played the role as well and it is because Ryan Reynolds would not be believable as a unpopular kid who hangs out in the library. Ryan Reynolds was too good looking (Nicholas is too but not in the same stratosphere as Ryan Reynolds). What I do disagree with the OP is to go on Nicholas Brendon's Imdb message board and trash his acting for being uncomfortable when the character itself would have been uncomfortable to begin with. Willow and Buffy, were equally, if not more, as uncomfortable in their roles. Why doesn't the OP make a same post on SMG and Alyson's boards? I think if Nick was uncomfortable in the role on Buffy: he wasn't alone and if anything, it actually made his role better as Xander in Season One. And the OP should be specific: where was he uncomfortable? Are you sure its not just the Xander character himself? I think this is the problem with people who bash Nicholas Brendon: they can't separate the character from the actor himself. I think that is the best compliment an actor can get and Nicholas Brendon WAS Xander and Xander WAS Nicholas Brendon.

He seemed so uncomfortable in the role. Luckily he grew into it during the second season.
I just finished re-watching Season One and I disagree, Nick Brendon was fine. Most all of them were a little rough around the edges at first, him no more than most and I'd say better than average.
Anthony Stewart Head was on a different plane, significantly superior than most the cast, but then again he was older and more experienced. I once saw James Marsters say something to the effect that his best moments on Buffy were when he could share a scene with ASH and not get blown off stage, you can see that from the very beginning of season one.
The one area I saw the most improvement from season one was the fight scenes. In season one they look like they're from a low-budget show on a struggling network, in some places they're just laughably bad. Later on that improved dramatically, but for those who go back and watch, some of those season one fight scenes are cringeworthy.
I was equally surprised at just how
good
SMG was as Buffy from the very first. She had the toughest part to play and basically nailed it from the beginning.

I believe Nick spoke about this in an interview once. He was basically playing Xander as a "regular guy" but Joss said something about how Xander was based on himself when he was younger. So Nick started studying Joss and playing Xander based on that. I think that's when the character clicked. When Nick started using Joss as his model for Xander.
Kitty: Is there anything you can't do?
Dr. Doom: Knit. I find it too repetitious.

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Your take away is that his acting, ONLY his acting, and during season one, ONLY season one, was terrible. The fact of the matter is when it comes to directing actors (which is really the main thing a director does), Joss Whedon is mediocre at best.
Anthony Head looked like freaking Laurence Olivier next to rest of the cast. and he was basically just cashing a paycheck. You can see it in the expression on his face,

He was excellent in the pilot episode! Which was never broadcast but is on youtube now, it features the original Willow, Riff Regan, who was replaced immediately thereafter by Alyson Hannigan

He was excellent right from episode one.

I thought Nick was great from start to finish as Xander
Old Toby,..the finest weed in the South Farthing

There's actors like Nicholas Brendon and Xander Berkeley, then there's star's like SMG or AH who have to learn to take the crap that comes with stardom.
I Take that Back

Pretty sure he was new to acting at the start of buffy. Maybe a couple guest spots but he didnt have a whole lot of experience.To be honest I never thought SMG or Alyson Hannigans acting was great either. Luckily they all grew into there roles by the time season 2 came around.