Former Australian Test quick Mitchell Johnson has come to the defence of England star Jofra Archer over his reaction to felling Steve Smith with a bouncer.

Key points: Jofra Archer was criticised after television footage showed him smiling as Steve Smith received treatment

Jofra Archer was criticised after television footage showed him smiling as Steve Smith received treatment Mitchel Johnson said that the reaction to Archer was "pretty poor"

Mitchel Johnson said that the reaction to Archer was "pretty poor" Former Australia captain Steve Waugh said Archer gave England an "X-factor"

Archer landed a bumper on Smith's neck on day four of the second Ashes Test, sending the in-form batsman crashing to the deck before eventually being ruled out for the rest of the Test and this week's third Test in Leeds with concussion.

But footage of Archer laughing with teammate Jos Buttler as Smith received attention sparked an angry reaction on social media.

But writing in his column for British publication iNews, Johnson said any inference that Archer "didn't care as much as he should have done" was wide of the mark.

Mitchell Johnson took 313 Test wickets for Australia with his left-arm fast bowling. ( AAP Image: Dave Hunt )

"Some of the criticism of Archer and the way both he and some of his England teammates reacted is so far wide of the mark I can hardly believe it," wrote Johnson, who has 313 Test wickets to his name.

"How, from the footage available, any journalist can deduce that he didn't care as much as he 'should have done' is beyond me.

"How do we know what went through his mind at that moment? We don't."

Johnson said Archer would have got quite an eye-opener over the expectations now placed on his shoulders from his incredible Test debut, and part of that would have been the reaction to Smith incident.

He said Archer may simply not have known how to react in the immediate aftermath.

"Placing a weight of expectation on him is a tough ask of a guy who is still fairly new to the big stage. One thing that may have opened his eyes is the dispute around his reaction to his blow to Smith's head," wrote Johnson.

"For me, I just don't think he knew how to react at that moment. To judge him without knowing the facts and on limited evidence is pretty poor.

Jofra Archer bowled with pace and hostility against Australia at Lord's. ( AP: Alastair Grant )

"Bowling with pace and hostility doesn't happen without the intent to do so. You need the desire to do it in order to go through all the pain that comes with bowling at extreme speeds.

"I can say with absolute honesty that I used to run in wanting to take the batsman's head off when I was trying to bowl a bouncer.

"That's not me saying I ever wanted to hurt anyone. It was simply a way to trick my mind and get up for the battle.

"When you're confronted with someone with the class and control of Smith, sometimes trying to make him feel uncomfortable is the best way to get him out. It's a tactic, and to accuse someone of not caring about hurting an opponent is low."

Mitchell Johnson said that he never wanted to hurt anyone, but caused batsmen plenty of pain during his career. ( AAP: Dave Hunt )

Archer's comments the following day reflected Johnson's, with the 24-year-old saying that he didn't know what to feel when he saw Smith hit the deck.

"To see him go down, everyone stopped and everyone's heart skipped a beat," Archer told the BBC on the fifth morning of the Test.

"After he got up and he was moving around, you breathe a sigh of relief."

Speaking to Sky Sports, he added: "Honestly, I don't know what I was thinking at the time.

"Seeing someone go down, you don't ever want to see anyone getting carried off in a stretcher or you don't want to see anyone missing a day or another game.

"Especially what happened a few years ago as well. It's never a nice sight."

'X-factor' Archer 'a real asset'

Archer bowled the fastest over by an English cricketer at Lord's, averaging 149.33kph, according to CricViz. ( AP: Alastair Grant )

Meanwhile, former Australia captain Steve Waugh says Archer has the "X-factor" that unsettles opposition batting line-ups, adding that the evenly balanced Ashes series would be decided by a few key moments.

Archer produced several spells of menacing quick bowling, hurrying the Australian batsmen up and forcing them into evasive action from deliveries that averaged more than 145 kilometres per hour.

He also hit Marnus Labuschagne, who replaced Smith on the fifth day and became the first concussion substitute in Test cricket, in the face grill of his helmet.

"It gives you the X-factor, knowing that you have that sort of bowler in your line-up when you can intimidate the opposition," Waugh told a Cricket Australia podcast.

"You can make things happen on a flat pitch and potentially get wickets in clumps.

"He's a real asset to England."

ABC/Reuters