Blur a background in Photoshop is easy with this feature. This uses the new feature of the select subject command found in the select menu. You should then have the cat (or person) etc selected and it probably has made a decent go of it.
However, there will probably be areas that it has confused with shadows etc and you can manually change the selection by using the lasso tool. Set the lasso to add or subtract from selection via the toolbar and then drag over the region you want to add or remove and with a little bit of zooming in and care, you can select the central figure that you want to remain sharp and the area you want to get out of focus will be unselected.
Go to the select menu and inverse the selection and now the required filter !
You can always use the Gaussian or surface etc, all fine but personally I like to use the gallery ones so go to the filter menu and blur gallery and go for the path one (it should be available but it is not available in all color modes.
The default pins will probably be not what you want. I like to apply the effect around the object so you can add the pins around the edge of the object, it can be done roughly but if you wish, you can carefully follow the outline of the object.
You can then change the speed etc of the effect via the panel and once you are happy with the speed etc then apply it.
You can also run this process a number of times as I often notice a part of an object that I missed first time around and after applying the effect in Photoshop, you can often see it as a glaring mistake.