Faf du Plessis takes the catch two metres inside the boundary. At that moment Ben Stokes is out. But du Plessis loses his balance; it's like the lusty power of Stokes is too much for him, and pushes him back. He falls over and his head slams into the padded boundary triangle. Stokes is now not out, and the ball is a six.

In this age of cricket, where players regularly take catches dancing around the boundary like science-fiction ballerinas, this is especially unfortunate. And because it is Stokes, that also means that the next two balls are bad. Stokes hits both for six, brings up his hundred, and the game that was in the balance for so long suddenly looks like it's for England. Du Plessis head-butted the rope; Stokes head-butted South Africa.

But to focus on this alone would be wrong. South Africa did many things wrong and this was not even the worst thing du Plessis did in the match. That would come later in the afternoon when he left a ball and was out lbw.

At the post-match TV chat, after South Africa were beaten on the final afternoon, du Plessis said: "It's very obvious to me the mistakes that we made." There were a lot.

The conditions were in South Africa's favour on the first morning. Four seam bowlers, all fairly different, the ball swinging, seaming and Vernon Philander being practically unplayable. But the rest of the attack were not great. It wasn't that they were terrible, they were just a bit short, a bit wide. England had an opener one bad game from being dropped and a debutant in their top three, but the pressure wasn't consistently there. It took them 30 overs to finally get it right, and by then they had Alastair Cook and Joe Root set.

Once they got it right, they even made Root struggle, but the ball wasn't new anymore and England made it through to the end of the day at least on equal terms, maybe ahead. Philander's illness got worse, meaning they would never really have him again in the match. The fifth bowler, Chris Morris, had to step up.

Morris came on to bowl the 69th over, and the tenth of the morning on day two. The first nine overs had gone for 27 runs and Morne Morkel had taken the wicket of Cook. This was a critical time in the match.

Morris is not a line-and-length bowler, he's explosive, and he goes for runs. And perhaps the most obvious thing about him is that he bowls very full. His first ball was full, and Stokes tried to nail it, but couldn't get it away. The next ball was a full toss, and Stokes hit it through covers. Morris followed it up with two half-volleys that Stokes smacked. There are going to be days when Morris doesn't work, players like him are risks. In the last Test, he paid off; in this Test, he went off.

That over went for 12. His final over went for 17.

The over of 17 included a six from Toby Roland-Jones, who is not an allrounder but is pretty far from a tailender. His known batting talent made South Africa's plan to suddenly put out nine men on the boundary for Stokes all the more bizarre. Stokes had hit no fours in almost 17 overs when Roland-Jones came in, and since that Morris over of 12 he had scored 22 from 52 balls. So you had a batsman that had slowed down, a lower-order guy who could handle the bat, a bowling attack that was chipping away, a pitch still offering help, and nine guys on the boundary. It was bizarre.

Stokes was on 68 when Roland Jones joined him. Thirteen overs later he had made 112, England had put on another 74, and the total had gone from par to decent.

That meant that South Africa had to start well. Part of that was going to be down to Heino Kuhn.

There is little doubt that Kuhn looks like he has the skill to play international cricket. He started his first-class career well, but had a dip for a few seasons that slowed him down. So when he finally got back into the form he had as a young man, he was over 30. This has been a tough series for batsmen; good bowlers and helpful pitches have made it a hard place to make your debut. Add to that du Plessis' suggestion that "day two, evening session was probably the hardest conditions you will face in Test cricket" and Kuhn couldn't have had a much tougher time to bat in.

"The mistakes that we made in this Test are very obvious things, so we don't have to go away scratch our heads about what to do"
Faf du Plessis

Dean Elgar had already poked at one he didn't need to, England hadn't bowled amazingly, but they were moving the ball and hunting. Kuhn looked composed, there were some cracking off-side shots, he was good in defence, and looked set. That is why it was so disappointing when he tried to flick a straight one across the line.

Kuhn is 33; he had replaced Stephen Cook, who is 34. Replacing an older flawed player who has some Test experience with another who is almost the same age and less experienced is the sort of decision that looks like a mistake. Kuhn may be a better player than Cook, he certainly looks more naturally gifted, but Cook's style (or lack of it) is more about getting in and holding on. Kuhn had to bat through the new ball; he had to negate the movement, he had to fight. Instead he gave it away. It wasn't just Kuhn who did.

"It's important you fight through it and limit the damage in those sessions, and we didn't do that," du Plessis said. South Africa were eight wickets down at stumps.

At the start of England's second innings, Elgar received an edge from Keaton Jennings in the slip cordon. It went fast to him, but burst straight through his hands and down to the boundary. The chances that South Africa, with a crook Philander, were going to rip through England for 150 and give themselves some hope were pretty slim. But this was that moment. Instead, Jennings played the sort of innings no South African from the top order managed first time around. He fought, clawed, and all but had to cut himself out of the shark's belly with a chainsaw.

Had South Africa continued to bowl amazing, keep the pressure on, and wait for England's fragile batting order to feel the pressure they might have been able to do some damage. But without Philander to pull them back, they bowled well for short times, and at others, they allowed England to get away. Much as they had in the first innings. Eventually they were bowling for a declaration. When that came, they had their last chance to save this game.

In the first Test, JP Duminy - Test average of 32 - batted at No. 4. Of course, in a perfect, just and beautiful world, AB de Villiers would be there. But he isn't.

Even the stars that are left are not shining brightly. Du Plessis averages 35 over the last two years. Even Hashim Amla, who blitzed the most recent IPL, averages only 36 in that time. The only other star in the line-up is Quinton de Kock, who in this series has had to move from No. 7 to No. 4 to fill shortcomings. In his 22 Tests, he has batted in seven of the 11 batting slots. The heart of this team is an incredible bowling attacking that will win them Tests even when their batsmen fail. They also have the battlers Elgar and Temba Bavuma, who are great when it's tough. But to win consistently, they need class around them.

On the fourth afternoon that class was terrible. Amla left a ball off the middle of his bat to slip. De Kock was beaten by his own footwork as much as he was a fast full one from Stokes. And du Plessis, the man who is known around the world as someone who draws Tests that no one thought could be saved, shouldered arms. He didn't play a shot in the second innings, with his team having lost two wickets in the last two overs, he raised his arms and watched England win the Test.

Du Plessis faced eight balls this match, he left four of them, and two of those got him out. That's not just a mistake, that's the same mistake twice. And that is what South Africa did; they didn't just make mistakes, they consistently made the same mistakes.

"The mistakes that we made in this Test are very obvious things, so we don't have to go away scratch our heads about what to do." That's how du Plessis put it. Before Old Trafford there will be no head-scratching, and at Old Trafford, hopefully, there will be no head-butting.

Jarrod Kimber is a writer for ESPNcricinfo. @ajarrodkimber