Here's a super easy way to see the lag in this game is persistent. Take a spell that takes more than 1s to cast, and just put auto run on and keep on try to cast that spell while running and see how far the spell casts. I picked Foe's Requiem (3.00s), and I range between 1.80s to 2.40s left before it is interrupted. That means it takes 0.6-1.2s before my client realizes that I cannot cast a spell while running continously. That's how far behind your client is compared to what actually happens on the server. There's no skill involved in this particular action, since I'm just running in a straight line and seeing when the spell stops. There is certainly no in game mechanics that'd allow you to cast a spell while running. I tried jumping and mashing random other buttons and they've no discernible effect on the time before the spell gets interrupted.