I'm sorry I fell asleep last night, it was very late.
The order is apparently silent regarding any specific obligation towards maintaining the child's extracurricular activities during his parenting time, so we have to look at general principles.
Firstly, I'm getting the impression from you that perhaps you don't know exactly what the court order had said, and in fact you weren't sure if there even was one. Such a long order is usually one carefully drafted by the lawyers and submitted as a consent order. I say that because judges don't normally draft a six page order of their own volition because they are people too and don't like writing more than they have to. Please be reminded that custody is about decision making authority only, and joint custody means that the two of you have to agree on major decisions regarding the child's upbringing which includes his enrolment and attendance at extracurricular activities.
You have joint custody. This means that with equal decision making authority, you should by definition be able to discuss this with the father in a rational way. If you can't talk without getting into an argument then joint custody isn't the right arrangement, but joint custody is what you have. Perhaps you should send dad an email so that you can compose it, think about it, and ensure that it has the right tone. In the email you should cite the facts, remind the dad that with joint custody comes the obligation to work out disputes in a child focused manner, and that you'd appreciate hearing from him that he's going to facilitate the hockey but if not then why not. Make sure that the email, if you send it, is respectful and not argumentative or inflammatory.
If father is resisting the hockey because he doesn't believe that the child wants to then tell the father that the child wants to go and that the child needs consistency, and that you two need to discuss the issue. Obviously, the child derives far less benefit from hockey if the child is only attending it half the time. Further, if the child is starting to say that he doesn't want to go to dad's because of this issue, tell father that and say that as a family this stalemate has to be worked through for everyone's benefit as a family.
Look back at the history since the separation. Was the child always in hockey? Prior to this order being made, was dad taking the child to hockey? If the answer is "yes", then father shouldn't be unilaterally changing the status quo of the child's attendance at extracurricular activities. While it's true that the order doesn't compel him to do so, and you cannot tell father what to do on his time, this hockey issue is about the child's extracurricular activities which is as much a custodial matter as an access matter. Thus, you can write to father that after consulting with legal counsel, you've been urged to write to him to make best efforts to resolve the dispute in an adult fashion as behooves custodial parents.
Again, ask dad specifically for all of his reasons for not wanting to take the child. If father says that he doesn't want to give up all his weekend time for the child's hockey, that's understandable. Offer him some more time so that each of you is sacrificing time with the child to facilitate the hockey. The order is the order, and it's what's to happen if the two of you can't agree; by insisting to stick to the order, whoever is insisting is thus saying that there's no compromise on the particular issue. If there's no compromise then that's fine but there should still be a discussion which is rational and child focused.
Remind father that the child wants to go, and that by denying the child then father is putting his relationship with the child in jeopardy; remind father that the child wants to go to hockey and if you two parents are going to change the child's attendance at extracurriculars then that's a custodial matter which you ought to be discussing in good faith.
That all sounds great in writing. I'm recommending the email because you'll have a record of it and of his response if he does so by email too. I'm assuming that the order doesn't have any "dispute resolution" mechanisms built in such as using a parenting co-ordinator in the event of a dispute. If there is any such thing in the order then please let me know, although I'll tell you that you have to avail yourself of that option as a next step.
Before you finish writing, you need to decide on whether this issue is important enough to you and the child that you're willing to take it back to court, because that's what you'll need to do if father digs in his heels. Don't threaten dad with court, but you could say that the two of you should be getting off to a better start than this so soon after a court order, especially since it's a joint custodial arrangement.
If dad is making his decision based on emotion, you won't get him off that by being emotional yourself and pleading for him to do the right thing. He already thinks he's doing the right thing by asserting his rights to manage the child's time while the child is in his care. You're not going to get him to change his mind by calling him a jerk. Instead, be super rational and objective, keep it respectful and concise, don't raise any other issues.
You can't literally make him take the child to hockey. But if father won't do it then you either have to let it go or take it back to court.
Lastly, the child is only nine. Don't put the child in the middle by having the child beg dad to take him, but if father wants to hear from the child that the child wants to go then you're in a tough spot. Perhaps before you write, ask the child if he's told his father that he wants to go to hockey or not and that you won't be upset either way, that you're trying your best to work this out with dad but that you need to know 100% that the child does want to do the hockey. Remember that children lie and will tell their feuding parents what each parent wants to hear in order to not be directly involved, it's always possible that the child has in fact told dad that he doesn't want to go; if father cites this reason then don't assume that father is lying. That happens all the time for a variety of reasons, and is an indication that you and father need better communication skills because you're allowing the child to play the two of you against each other. Feel free to say that in the email too: joint custody is only going to work if the two of you can communicate and give each other the benefit of the doubt.
So in summary, if father won't take the child then he's not in contempt of the court order, and you can't make him take the child. But you have joint custody so you should make every effort to work this out reasonably and hopefully also set a precedent for resolving future disputes. If you can't work this out then you either have to let it go or take it back to court, and you should discuss that option with the lawyer you had. Lastly, you need to make sure that you know what's in your order and that you understand it because there's no point in arguing with father about issues which are already addressed in the order.
If you don't want to write, then perhaps there's a mutual friend or someone like a family member who has the kind of relationship with each you that they might facilitate a discussion about it in person and help mediate.
Does that all make sense? Please reply if there's more to discuss. I'll be here. But if you're satisfied that I've answered you then I'd appreciate a positive service rating please, which is how I get credit from the site for the time spent on your matter. In that case, keep an eye on your credit card statement to ensure that your initial refund was processed and that you were charged only once more for concluding our discussion. But if there's more to talk about then please get back to me before rating.