Hello. Our 9 month old staff our pup has started trying play by chewing and tugging on his lead when we are out walking. He does it more with me than my husband and as he's quite strong I struggle to stop him. I also think he thinks I'm playing with him when I'm actually trying to get him to stop 
We have no idea why he's suddenly started doing it but it's making my walks with him often stressful.
Anyone have any tips on how to nip this in the bud? The only way I get him to stop is by holding him down until he calms down and letting him up and if he carries on doing it I repeat until he stops but I feel really mean doing this and I'm sure there must be another way to get him to stop.
First time having a puppy/dog although my husband has grew up with dogs.
Thanks