Why do you think he changed his action? Is it due to his injury or anyone advised him to do it? Changing natural action is never a good idea.
Waqar was getting a lot of flak for being ineffective, and there were (stupid) complaints that Naseem was spraying the ball around a bit. He had some minor technical issues that needed to be adjusted like hip alignment and direction of the feet, but rather than focus on these, Waqar shortened his runup (the primary reason for the drop in pace) and told him to focus on line and length, channel bowling.
Naseem’s strength has always been the short ball and bouncer, as well as pitching it up — after terrorizing Australia A he showed some glimpses of this against Australia (despite returning bad figures) and then Bangladesh and Sri Lanka where he excelled, though the opposition is not a good benchmark.
Against England, he did not do well. He bowled some very good balls and got Joe Root out, but he was also recovering from injury and had not bowled in months, combined with Waqar changing his style of bowling to focus on the corridor channel.
As a result, despite us being in a position to win the first Test, Naseem did NOT use his strength and employ the short ball against Woakes, which he had gotten out to something like 6 times in his last 8 innings.
By the third test, Naseem was bowling with a shortened runup (Waqar’s out of the box idea to help him with his control).
Now in New Zealand, his side on action has become slightly more front on and open chested, which I presume is to help with injuries by reducing the load on his back. However, there were ways to reduce this load NOT by making such a big change but rather by improving his hip rotation when he enters delivery stride, also making use of his non-bowling arm to pivot better. He actually used to do the second (use of non bowling arm) already after he did 1 year rehabilitation at the NCA following a back injury in 2018, but Waqar has actually reduced the use of that too, now that his chest faces the batsman more, and the need to pivot using the non-bowling arm for stability is less required. In other words, the minor technical changes that should have been done were not done, and instead his runup shortened and action modified. I am not a bowling expert, but this is just what I’ve been able to gather from my untrained eye.
What people (I’m talking non-Pakistanis too like Holding) used to call a beautiful bowling action that reminds of Lillee (in style, not in ability), now looks a shadow of what it used to be.
These changes have taken a toll on Naseem’s zip, which he used to generate his pace (further exacerbated by the shortened runup) and which last year troubled the likes of Usman Khwaja, Marcus Harris in the Australia A game and David Warner in the Test (out on a no ball in his 30s, before he made his 300, and then again got out to Naseem - fair enough, not a good performance on debut, and I was never one of those calling him Fred Trueman, simply one who thought he had potential).
There is a reason he was being compared to Jofra Archer, not just by Pakistanis but English commentators too who were criticizing Archer for not being able to maintain his speeds in his second and third spell while Naseem
was able to do so.
The proof is in the pudding. I am not denying that the Naseem you see now is a very bad bowler. But I also believe that if he were to go back to his natural runup (one of the things you never or very rarely change in a bowler), and continue to bowl side-on with better hip rotation and use of the non-bowling arm, he can be much more threatening - at this point, I will not mind if he is criticized and fails to improve.
I just don’t appreciate the majority of people on this forum and on social media kicking a kid when he’s down, that too through no fault of his own.
But their is that Xfactor about him & that amazing actin that keeps your hopes up
) He likes to see fear in batsmen's eyes.
