Can a pitcher use an infielders glove?/ glove without closed web?

In this case: size matters. So does color. No pitcher's glove can have any white on it. The size is dictated by the rule book for your league, conference, state. etc...but, you've got a small glove so you should be fine.... be sure to oil it generously - Neets Foot Oil - put a baseball in the pocket and then wrap is tight with rubber bands....

color shouldn't be a problem, but every umpire is different. The open webbing is a concern as your grip will be exposed to the hitter, or a spotter from the opposing dugout. My advice; look to get a inexpensive back up, with a closed web 12"

Yes. Different leagues have different rules. In Little League the glove for a pitcher can't have any white on it because it can distract the batter. As long as the glove is only black or brown it should be fine.

Yes. The reason many pitchers do not use an "open web" glove is because the opposing team can spot changes in your grip and know what pitch is coming. If you notice, even with closed-web gloves, many major league pitchers (Clayton Kershaw is one) hold their glove as wide as possible while in the "set" position to hide his throwing hand. Future Hall of Famer Greg Maddux taught him this, telling him that if you close your glove tightly around your pitching hand, batters will notice the 'wiggle' when you shift your grip.

yes. it depends on what league you are in. different leagues have different rules. If I were you I would check the rules just to be sure.

Yes. It is just frowned upon, because a good hitter will pick up on things because it isn't closed.