I want to identify many number fonts used in soccer jersey. It's easy to post pictures and ask for help but I would like to learn how to do it on my own. Can you recommend any tool ? I saw identifont by appearance, but they ask many questions about letters and I have only numbers.

Are you sure?

OK then here we go. But be aware that most if not all of these typefaces used on soccer (or any other sports) shirts are variations on existing types or a completely custom made design. For branding and merchandising reasons and ... to prevent people like Matt to start a counterfeit merchandising business. So you will not too often find a perfect match. Unless someone has made a font to simulate a certain club's logo.

So how to match a font to a pict:
1. The eye and the memory. See a font and know its name. There are some that have the power. Some.

For those that don't:

2. The letters/numbers in these shirts' picts are most always deformed so you have to look at specific - uncommon - details to decide whether a font is a possible match.
3. The better font sites have their fonts categorized. Most clubs' fonts will fall in the category sans or inline or multiline. These are very generic categories so you will have to browse a lot of pages on these sites.
4. You can also do a perspective correction on the pict - Photoshop, PSP, name it - and if needed improve definition and contrast - and use What the Font to find a match. WTF, however, is not always that reliable. That is, it can be very picky on the quality of the sample and can turn out ridiculous results, or, be smack bang on. WTF needs positive images. That is, the letters/numbers (no zeros) darker than the background. Otherwise it will consider the whole pict as one. Sometimes - often - most times the pict quality is that bad that you need to reconstruct a typical letter/number. Illustrator, Corel Draw, or even PowerPoint can be of use.
5. DIY. That is, build a - large - font collection. Go font hunting, look at the download links of font sites and put a spider on them - have a coffee. The better font sites will not allow you to do this. Or ask Big Brother for "index of fonts". Spider'm. Run a font renamer to get the real font names. Merge all your work into one or more collections/classifications and run the result of 4. through something like Font Matcher and have another coffee. Or two.

You will probably end up with no real match. See above. But sometimes you can be lucky and end up with something that is close.

So, are you sure? With these soccer/sports things it is often easier and quicker to make your own.

¡Bueana suerte Fernando!