Protecting what’s dear to you: Wyald’s encounter
There is a lot happening in this section, including things not necessarily relevant to Guts and Casca themselves, so I will cut it short — or at least, as short as I can.
Guts is pushing himself to kill Wyald no matter what. In my opinion, he does this for these major reasons (among others):
- directly protect the Hawks: he did see how the Hawks got slaughtered when he encountered Zodd the first time.
- avenge the farmer people that helped the Hawks by providing them carriages. They were slaughtered and raped by the Black Dog Knights. Wyald throws one of their bodies at Guts, and then we see him turning around to attack him in rage. The facial expression he has here is similar to how he looked at the torturer when he reached Griffith in his torture chamber.
- Wyald almost got hold of Casca to violate her. Letting him stay alive would endanger her sooner or later.
In other words, with his own sword, he wishes to protect as many bystanders and innocents as possible — a theme that occurs in Berserk many times.
We also see how Casca is extremely worried for Guts’ safety and life. She will tell him off for that in the aftermath as well.
Let’s take a look at the relevant interactions in this section:
 After they escaped the tower, Guts, Casca and Griffith managed to get hold of a carriage, which was lend to them by well-meaning farmers. They all hop onto it and we get to see this brief interaction here.
Judeau is holding the reins while Guts and Pippin are on horseback as defense. Griffith takes seat at the back of the carriage together with Casca. As she settles down, she contemplates how she cannot find the words after all she has done for him. Remember, Griffith can’t talk and this would be the chance to tell him all the hardship she has been through for his sake. But, she does not bring out a single word.
Instead, we see her grabbing onto his shoulder. It appears like Casca turns all quiet when she is emotionally affected by something, unable to communicate her (sometimes intense) emotions.
Of course, Guts is watching and looks away. Someone is jealous! Turning around in jealousy because he can’t stand seeing them like this he also has done before: see the Campfire of Dreams chapter.
After that they take off. Wyald and his men arrive in the meantime, deciding to pillage the farm and rape the women (they are the same ones that helped the Hawks). They would soon catch up to Casca and the others.
They have set up an explosive trap at the bridge but cannot use it because of the little distance between them and the Black Dog Knights, as Judeau points out. So instead, Guts decides to distract them to buy them some time.
Before Guts is riding off to fight Wyald, Casca tells him not to be absurd again, like he was that one time (we can assume she is referring to the 100-Man-Slayer scene). Guts tells her that he learned his lesson. At best, he is taking what she is telling him to heart, at worst, he’s only trying to make her worry less.
Look at Casca’s reaction when he says this: She is clasping her hands together, it appears she is being very thoughtful here. And look at Griffith taking note of her reaction, too.
Guts in this instance indeed takes her advice to heart, because he actually retreats after they prepared the explosives to blow up the bridge in order to shake off Wyald and his men.
However, after that, there was no escape anymore.
 Soon enough, Guts challenges Wyald in a one-on-one battle, knowing that he must be a monster after all he has seen. This is when Wyald remarks how Guts seem to know something and shows his true nature, transforming into an apostle.
Throughout their fight scene, we see a worrying and anxious Casca as Guts gets beaten up by Wyald pretty badly.
 One interesting thing that happens between Guts and Casca is when the Hawks manage to distract Wyald as Guts lays unconscious on the ground. Casca runs towards him and attempts to wake him up.
Griffith of course notices how much Casca worries about Guts as she tells him to get back up. She is shaking in anxiety as she notices how he is not responding to her voice. Note Casca’s expression in the bottom left panel, as she grabs unconscious Guts by his shirt and pulls him up to her: she is completely on edge here. She technically “lost” Griffith already and now she is absolutely frightened and distraught over Guts.
In despair, she is attempting to slap Guts awake, telling him to wake up and open his eyes. She’s not going to let him die by the monster that is Wyald. Finally, she brings up the fact Guts wanted to take her with him. The fact she does so shows us that she is scared of being abandoned and left behind. Later in volume 12, chapter “Requiem of the Wind”, she would state this as well: “I wanted someone to be near me“.
Her new dream and hope Casca found after the waterfall scene is now being threatened, with Guts’ laying incapacitated (dead?) on the ground. This is precisely why she will tell him off after the battle, too.
Of course, what is happening doesn’t escape Griffith either. He is watching them in the distance as he is being carried away by his men.
However, Wyald soon notices that Casca is present and does not hesitate to try and violate her, ripping off her armor and clothes (even though I admit she is really nice to look at, I think to have her half-naked here is — in my opinion — unnecessary self-serving fanservice on Miura’s part). Guts wakes up last second to save her while chopping off Wyald’s apostle private parts.
But hey, at least Guts managed to save her here! He mentions how hard she has been slapping him awake. Thanks to her, he is back up on his feet. After telling Casca that she will distract him looking like that, he also tells her that he intends to take on Wyald all by himself. Casca pushes him to hurry and escape instead.
Guts does not listen. He has the intention to take Wyald down, given that he is a direct threat to Casca. I mean, Guts has seen what happened to the women at the farm and just barely saved Casca from being violated. So in order to protect Casca, he breaks the promise he has given to her earlier: namely to run rather than to fight, even though he first actually lived up to it.
 As Guts is taking on this huge monster all by himself, he again gets beaten up really badly. Casca cannot stand the sight of it and looks away.
 She is trying to get close to Guts as they fight, but Judeau holds her back. Rightfully so — because if she really comes any closer, she would fall prey to thirsty Wyald. She contemplates how it’s alright to run away sometimes.
The answer in her question “Why does he always have to fight?” probably lies in the fact that Guts does have a sense for justice and empathy: Him seeing literal monsters injuring, killing or raping innocents motivates him to avenge them — and by killing these monsters, he prevents them from hurting even more people. Loved ones included.
To kill Wyald Guts resorts to a different strategy, which is quite cunning if you ask me. First, he hides and makes one of the bodies stand up to make the impression he is hiding behind a tree. Then, he instead attacks from above. However, if you look closely, he is not going in first, but throws a log at Wyald that is dressed in his armor. You see him appearing behind the log instead. Only after the Apostle slapped away the log he realized Guts’ scheme, but it was already too late for the him to parry properly. That means, Guts was not thinking just two steps ahead — he was thinking even a third step further.
Wyald attempted to protect himself with his hand and as Guts’ sword pierces through it, he breaks his blade. With the broken blade, Guts rams the stump of his sword into his throat. We then see at least three pages dedicated how mercilessly Guts is choking Wyald with the blade stuck in his neck. He also rams his smaller knife into his left eye. Really nasty and gruesome if you think about it.
Once again, seeing this I can’t help but think of how gruesome Guts was to Donovan when he avenged himself back in volume 4. Repeatedly, having the chance to take down monsters turns Guts into a monster.
As Wyald trembles and attempts to fight back, he hits Guts against a tree, with the result of Guts falling and sliding down on it. Then, Wyald collapses.
Casca is not wasting time and instantly rushes to Guts who is laying beside the tree. Her face seeing that he is still alive says it all.
After the fight
 Now it’s time to tend to the wounded. Judeau is applying bandages to Griffith’s sore body and Casca takes responsibility for Guts’ wounds. Being as strict as she is, she tells Guts off for taking on Wyald all alone.
Guts being the cheeky bastard as he is, is making fun of Casca’s strictness, comparing it to Wyald. Well, she doesn’t take this joke lightly, pulling tightly on the thread she just sew to stitch his wounds. The expressions on that panel are priceless and it’s of my favorites in this manga.
She notes that Guts has gotten stronger compared to last year and is lecturing him how he still does not know when to quit. All while Guts is more than happy that he won the battle at all, Casca insists on the severity of this issue. Guts is gambling with his life, playing around like a child.
However, to Casca, it is not a play at all. Reverting back to her role as a lover and showing some vulnerability, she reveals that she is extremely worried about his life and well-being.
Note how she tells him to die on the battle field. She has told him this before in spite, but this time, the context is entirely different. She doesn’t say it because she actually wishes him to die -— quite the opposite so. She says so because she is upset he is disregarding her concern and worry for him while he is fighting to death. It feeds her anxiety in a time when she needs someone to be there for her.
I think Guts got the hint, judging by the old pout he makes here.