Most folks that hunt will either say that the "come" command, or the "whoa" command is the most important. It really depends on the person.
Come is the command that brings the dog to you, whoa is the command that brings you to the dog. Whoa however, is a command that can save your dogs life.
When the command whoa is given, it's a no nonsense command. It means stop and do not move one iota, and not to be confused with "stay". Whether the command is given to lock the dog on the bird, and keep him out of the field of shotgun fire, or stop him dead in his tracks if he is getting near anything dangerous, like the road oscar crossed, matters not. If you can lock him in one position, until you can re-establish control, he is a much safer boy.
To be "solid" means that Oscar is 100% on that command. He does it every time without hesitation and regardless of distraction. When the command is given, he locks in mid stride. (Not having one of my Vizsla's absolutely solid on this cost me in excess of $3000.00 in vet bills when he got clipped by a car. Luckily he lived another 8 years, and I was able to learn from my mistakes with him.)
The important thing to take away from your event today is that Oscar displayed that he is not solid. Prior to this he was emotionally dependent on you and that was your mechanism of control. Now he's a little older( mature),and becoming less dependent on you. He was thinking for himself, and making his own decisions. Some folks term this "out of control". I don't though. Out of control is something completely different to me.
At 7 months old, in an open area, Oscar should still be on a check cord/long leash. He needs you to be making his decisions for him for awhile longer. That he needs to go back on the leash is not a reflection on you. It's just where he is at now in his mental and physical development.
Work the whoa in the backyard. Whether you use a "whoa pole", a sling, a "whoa barrel" or a training table is kind of up to you. I prefer to use a combination of the table and the pole. It's also time to work in some of the other commands, like heel and fetch.
One exercise I like to use to test where the dog is at goes like this; I walk the dog at the heel to an open area with a frisbee or two in my hands that I am tossing ahead of me as we walk and picking them up myself. I'll then stop and put the dog on stay. Throw the frisbee, and then command fetch. Halfway to the frisbee I whoa the dog, walk to him and re-command fetch. This is a high pressure sequence,and it takes awhile to get a dog to this point. Once at this point however, the transition to live birds is easier. It's a good sequence to break down into individual components and work on.