If you build your character around protecting your teammates.
Paladin Oath Of The Crown (Sword Coast Adventurers Guide, p. 132-133)
Starting at 7th level, when a creature within 5ft of you takes damage, you can use your reaction to magically substitute your own health for that of the target creature, causing that creature not to take damage. This damage to you can’t be reduced or prevented in any way.
Any paladin can take the Protection fighting style
When a creature you can see attacks a target other than you that is within 5 feet of you, you can use your Reaction to impose disadvantage on the Attack roll. You must be wielding a Shield.
These are two examples, there are many ways to protect other players. The Oath example seems to closely match your question about taking a hit for a teammate. A similar one is the Aura of the Guardian in the Oath of Redemption Paladin
Aura of the Guardian
Starting at 7th level, you can Shield others from harm at the cost of your own health. When a creature within 10 feet of you takes damage, you can use your Reaction to magically take that damage, instead of that creature taking it. This feature doesn’t transfer any other Effects that might accompany the damage, and this damage can’t be reduced in any way.
At 18th level, the range of this aura increases to 30 feet. (Xanathar's Guide to Everything, p. 39)
For a non Paladin way to help a teammate the College of Lore Bard has Cutting Words
Also at 3rd level, you learn how to use your wit to distract, confuse, and otherwise sap the confidence and competence of others. When a creature that you can see within 60 feet of you makes an attack roll, an ability check, or a damage roll, you can use your reaction to expend one of your uses of Bardic Inspiration, rolling a Bardic Inspiration die and subtracting the number rolled from the creature’s roll. You can choose to use this feature after the creature makes its roll, but before the DM determines whether the attack roll or ability check succeeds or fails, or before the creature deals its damage. The creature is immune if it can’t hear you or if it’s immune to being charmed.