sportlich
athletic
Relating to sports, good at sports, or physically active and trained.
Er ist ein sehr sportlicher Typ und fährt jeden Tag mit dem Rad zur Arbeit.
He is a very athletic type and rides his bike to work every day.

sporty / athletic
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athletic
Relating to sports, good at sports, or physically active and trained.
Er ist ein sehr sportlicher Typ und fährt jeden Tag mit dem Rad zur Arbeit.
He is a very athletic type and rides his bike to work every day.

The adjective 'sportlich' (sporty/athletic) is derived directly from the noun 'der Sport' (sport). The ending '-lich' is a typical way to form an adjective from a noun.
Sie interessiert sich für alle sportlichen Aktivitäten.
She is interested in all athletic activities.
The meaning of 'sportlich' (sporty/athletic) depends strongly on the context. If it refers to a person, it is about fitness. If it refers to behavior, it is about fairness. If it refers to a goal or plan, it means 'anspruchsvoll' (demanding/ambitious).
Mein Bruder ist sehr sportlich und geht dreimal pro Woche ins Fitnessstudio.
My brother is very athletic and goes to the gym three times a week.
In this meaning, 'sportlich' (fair/sporting) does not describe the body, but rather someone's character or an action. A 'sportliche Geste' (sporting gesture), for example, is fair behavior toward a competitor.
Er hat seine Niederlage sehr sportlich akzeptiert und dem Gewinner gratuliert.
He accepted his defeat very fairly and congratulated the winner.
In connection with clothing, the adjective is often nominalized. The phrase 'etwas Sportliches' means 'sportliche Kleidung' (sporty clothing).
Für die Wanderung solltest du dir etwas Sportliches anziehen.
For the hike, you should put on something sporty.
The meaning 'anspruchsvoll' (demanding) or 'ehrgeizig' (ambitious) is mainly colloquial. It is often used to describe a tight schedule or a difficult goal.
In nur zwei Tagen umzuziehen, ist ein wirklich sportlicher Plan.
Moving in just two days is a really ambitious plan.
difficult
'schwierig' and 'sportlich' can both express that something is not easy to achieve. 'schwierig' is the normal and neutral word for tasks, questions, or goals that require a lot of work or skill. 'sportlich' is used colloquially when a goal is very ambitious or tight, for example a deadline, a plan, or a number. It often sounds a bit more casual and can also show that you are accepting the challenge. For real problems or complicated content, 'schwierig' is usually more precise.

Der Zeitplan für das Projekt ist sportlich, aber wir versuchen es.
The schedule for the project is ambitious, but we will try.
Die Aufgabe ist schwierig, deshalb brauche ich mehr Zeit.
The task is difficult, so I need more time.