Cards in Homerun Clash are assigned grades according to its rarity and value.
In order of ascending value, card grades are divded into Normal (Gray), Minor (Blue), Major (Green), Allstar (Yellow), Legendary (Purple).

Each card grade can be upgraded to different maximum level caps.

Normal (Gray): Lvl. 20
Minor (Blue): Lvl. 15
Major (Green): Lvl. 10
Allstar (Yellow): Lvl. 8
Legendary (Purple): Lvl. 6

Likewise, the number of cards required to upgrade to max level is also different for each grade.