Use "Hidden Armory" to search this card, but only if you feel the restriction of Normal Summoning/Setting isn't that harmful (which can be, if you currently control no "U.A." monsters and/or you want to trigger the effect of "U.A. Stadium").
If a card/effect is activated that would destroy this resolved card, Chain the effect of "U.A. Midfielder" to that card/effect (assuming that monster isn't equipped with this card) in order to protect this card.
Similarly, if you attack with a monster equipped with this card (other than "U.A. Mighty Slugger") and your opponent activates a card/effect that would destroy, banish, or shuffle the attacking monster into the Deck, Chain the effect of "U.A. Midfielder" to save this card, while also possibly allowing you to continue your attacks this turn.